Tow/haul or not tow/haul that is the question

[Will_T]

At 7500lbs I would personally use TH, which means you won’t be in 6th at 60.

You will rarely have to use the ERS to lock out gears, and when you do it’s usually due to rolling hills or long steep slow hills.

Mine in Tow-Haul with the 8,000 lb. TT will cruise in 6th all day at 60 to 65 mph and about 1,200 to 1,300 RPMs unless I encounter a decent hill. If I lock out 6th, then the RPMs go up to 1,600 or maybe a bit higher and it stays in 5th unless I really have to slow down in traffic on a decent uphill. I have not noticed any mpg difference locking out 6th either which seems odd since the RPMs are higher.

Are you folks saying that there is no real advantage to locking out 6th at 1,200 rpm to run in 5th at 1,700 RPMs. I guess I just feel like the slightly higher RPMs are better but that may be out of date thinking. I do like that when I lock out 6th there is not any of the 6th to 5th and back to 6th shifting that happens when I just leave it in 6th. Regardless of whether it is really necessary, I think I like it better with 6th locked out. So, if it is not doing any harm (?) to run for hours at 1,700 RPMS instead of 1,200 RPMs, I think I will stay with it. I do now always try to remember to use Tow-Haul when towing so the numbers I describe are with Tow-Haul on.

 

[AH64ID]

Mine in Tow-Haul with the 8,000 lb. TT will cruise in 6th all day at 60 to 65 mph and about 1,200 to 1,300 RPMs unless I encounter a decent hill. If I lock out 6th, then the RPMs go up to 1,600 or maybe a bit higher and it stays in 5th unless I really have to slow down in traffic on a decent uphill. I have not noticed any mpg difference locking out 6th either which seems odd since the RPMs are higher.

Are you folks saying that there is no real advantage to locking out 6th at 1,200 rpm to run in 5th at 1,700 RPMs. I guess I just feel like the slightly higher RPMs are better but that may be out of date thinking. I do like that when I lock out 6th there is not any of the 6th to 5th and back to 6th shifting that happens when I just leave it in 6th. Regardless of whether it is really necessary, I think I like it better with 6th locked out. So, if it is not doing any harm (?) to run for hours at 1,700 RPMS instead of 1,200 RPMs, I think I will stay with it. I do now always try to remember to use Tow-Haul when towing so the numbers I describe are with Tow-Haul on.

When using TH the truck won’t shift into 6th until 65 mph, and that’s enough rpms for most terrain until hit bigger hills and then the truck will downshift on its own.

I’ll only lock out 6th, or any gear, for rolling hills where the truck is constantly shifting on me.

The 68RFE has a lower 5th, so you will see a bigger rpm increase from 6 to 5 than I will.

 

[Will_T]

When using TH the truck won’t shift into 6th until 65 mph, and that’s enough rpms for most terrain until hit bigger hills and then the truck will downshift on its own.

I’ll only lock out 6th, or any gear, for rolling hills where the truck is constantly shifting on me.

The 68RFE has a lower 5th, so you will see a bigger rpm increase from 6 to 5 than I will.

I see, yes, the shifting into 6th only once 65 mph is reached must be a difference between the 68RFE and Aisin also. Or at least a difference with my specific truck. Even in TH my truck will cruise at 60mph in 6th all the time and at 1,200 or max 1,300 RPMs. I have had it even shift from 5th to 6th when closer to 50 or 55 mph if I let off the accelerator. The only time it will stay in 5th when 60 mph or above is if I am accelerating or uphill. If on level ground, as soon as I am anywhere close to 60 and back off, it shifts to 6th. It will run on flat open highway all day at 60 mph in 6th gear and 1.200 RPMs if I let it. Again, all of this is in TH mode with the TT. Empty with no TH, it will go into 6th all the time at 40 or 45mph or so. It is actually kind of annoying, so I often lock out 6th then also. Different trucks run differently I guess.

 

[Jimmy Dean]

Really the best reason to use tow haul is for the better exhaust braking for the diesels not so much the gear selection

Experienced this last weekend towing around 5.5K….phenomenal exhaust braking. It would be nice if it worked under 20mph…tuners please hurry on the 22+…

 

[AH64ID]

I see, yes, the shifting into 6th only once 65 mph is reached must be a difference between the 68RFE and Aisin also. Or at least a difference with my specific truck. Even in TH my truck will cruise at 60mph in 6th all the time and at 1,200 or max 1,300 RPMs. I have had it even shift from 5th to 6th when closer to 50 or 55 mph if I let off the accelerator. The only time it will stay in 5th when 60 mph or above is if I am accelerating or uphill. If on level ground, as soon as I am anywhere close to 60 and back off, it shifts to 6th. It will run on flat open highway all day at 60 mph in 6th gear and 1.200 RPMs if I let it. Again, all of this is in TH mode with the TT. Empty with no TH, it will go into 6th all the time at 40 or 45mph or so. It is actually kind of annoying, so I often lock out 6th then also. Different trucks run differently I guess.

Interesting, I was under the impression TH locked 6th gear out below 65 on both transmissions.

Are you running oversized tires? 60 in 6th should be just shy of 1500 rpms, not 1200. 1200 in 6th is ~49 mph.

40 mph is under 1000 rpms, are you sure it shifts into 6th that slow?

 

[Brutal_HO]

Interesting, I was under the impression TH locked 6th gear out below 65 on both transmissions.

Are you running oversized tires? 60 in 6th should be just shy of 1500 rpms, not 1200. 1200 in 6th is ~49 mph.

40 mph is under 1000 rpms, are you sure it shifts into 6th that slow?

My HO will shift into 6th in TH under no/low load below 65, around 61-62 most times..

 

[Brutal_HO]

The sweet spot for the 6.7 is ~1900-2200 RPM.

You should not see any difference in mileage at low RPM vs that sweet spot, so keep the trans in a gear that doesn't hunt and doesn't lug the engine. Frequent shifts build heat just like TC unlock builds heat.

 

[AH64ID]

My HO will shift into 6th in TH under no/low load below 65, around 61-62 most times..

Interesting. Both my HO’s have been the same, 65 and no slower. I expected the 22 to shift sooner due to the 3.73’s, but it does not.

I’ve read numerous other folks state 65 as well. If I’m doing 60-62 out of TH and turn TH on the truck will downshift to 5th, both the 18 and 22.

 

[Will_T]

Interesting, I was under the impression TH locked 6th gear out below 65 on both transmissions.

Are you running oversized tires? 60 in 6th should be just shy of 1500 rpms, not 1200. 1200 in 6th is ~49 mph.

40 mph is under 1000 rpms, are you sure it shifts into 6th that slow?

Stock tires. On the next long tow coming up soon, I will pay close attention to the exact shifting and RPMs both in TH and not in TH and report back. I pretty much always use cruise on the highway with my smallish TT so what I have noted is with cruise and TH both on.

 

[H3LZSN1P3R]

Interesting, I was under the impression TH locked 6th gear out below 65 on both transmissions.

Are you running oversized tires? 60 in 6th should be just shy of 1500 rpms, not 1200. 1200 in 6th is ~49 mph.

40 mph is under 1000 rpms, are you sure it shifts into 6th that slow?

The 68RFE will shift to 6th as early as 55MPH with tow haul on

The SO cummins makes max tq at 1700 RPM. I usually keep it in the 1700-2000 RPM range

Any higher than 2000 is when it starts to really drink fuel its been that way for ever cummins i have owned

The HO makes max tq at 1800 RPM so id say the sweet spot would be relatively the same

 

[Blythkd1]

Mine goes into 6th right around 62mph, T/H on or off. The trans temp never moves regardless of T/H selection either so I assume it must be locking up either way. I towed a 10k 5th wheel through 50+mph winds in Wyoming the other day running in 5th gear and dropping to 4th at times to keep it moving and the trans temp never broke 165, which is pretty much just where it runs.

About the only difference I've noticed with T/H on is the aggressive downshifting when braking down to a stop. I know it changes the upshift points too but that part seems to be fairly inconsequential.

 

[jebruns]

The sweet spot for the 6.7 is ~1900-2200 RPM.

You should not see any difference in mileage at low RPM vs that sweet spot, so keep the trans in a gear that doesn't hunt and doesn't lug the engine. Frequent shifts build heat just like TC unlock builds heat.

But if the truck is not hunting, there's no need for it, just like the owners manual says.

 

[AH64ID]

Mine goes into 6th right around 62mph, T/H on or off. The trans temp never moves regardless of T/H selection either so I assume it must be locking up either way. I towed a 10k 5th wheel through 50+mph winds in Wyoming the other day running in 5th gear and dropping to 4th at times to keep it moving and the trans temp never broke 165, which is pretty much just where it runs.

About the only difference I've noticed with T/H on is the aggressive downshifting when braking down to a stop. I know it changes the upshift points too but that part seems to be fairly inconsequential.

Sounds like the C&C gets some different programming than the HO pickup, even thou it s the same trans.

Up shift points are very different, and effective, TH vs no-TH in a pickup. They are most noticeable at light throttle, with mid-high throttle they aren’t as noticeable and the HO motor has the power to pull thru the earlier shifts.

The Aisin really doesn’t ever change temp as long as the torque converter is locked.

 

[flan]

I’m in the run tow haul/full eb towing or not camp. I like the shifting strategy much better (less lugging in 6th) and aggressive exhaust braking. 65 is the 6th gear speed on my 68. I’m convinced the trans strategy is much improved after the CP4 recall and subsequent computer reflash.

 

[downsc123]

Interesting. Both my HO’s have been the same, 65 and no slower. I expected the 22 to shift sooner due to the 3.73’s, but it does not.

I’ve read numerous other folks state 65 as well. If I’m doing 60-62 out of TH and turn TH on the truck will downshift to 5th, both the 18 and 22.

This matches my exact experience as well

 

[Will_T]

Today I was driving the truck empty and accelerated to 45 to 50mph. Truck was in 5th. I then backed off a little on the pedal and the truck immediately dropped into 6th gear and stayed there as I continued for about a mile keeping it just over 45mph. Once I slowed down for some traffic, it shifted down. I know it does not do it at those low speeds in TH, but I am pretty sure I have seen it in 6th many times under 60 mph with the TT and in TH and maybe even with cruise on. I will test soon.

 

[Aketay]

If I have a trailer hooked to the truck, I run the in T/H. This is a 13,035 lbs parachute designed to destroy your mileage. When running one of these, I lock out 6th gear if it hunts. There have been many days that I get better mileage at 65 to 68 mph in 5th. T/H locks up the torque converter sooner to keep the fluid from heating up. The crisper shift aids in gaining speed when accelerating. The only thing I don’t like about it is when downshifting on steep grades it can get a little harsh, during slick conditions I’ll switch out of T/H and set the exhaust brake to always on. As far as the shift to 6th is concerned, it won’t do it until I’m done accelerating to speed. So sometimes it won’t shift until 70 mph but never before 60 mph.

 

[ppine]

I spent the week in the Sierra Nevada Foothills. It is steep country with a lot of curves and gulches. Some of the grades are over 20%. I used Tow/Haul while running empty with some good results.

 

[mountainears]

I live in the SN Foothills. I drive with full exhaust brake all the time. Sometimes I’ll turn on the tow haul mode when empty, but not often.


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[Blythkd1]

Sounds like the C&C gets some different programming than the HO pickup, even thou it s the same trans.

Up shift points are very different, and effective, TH vs no-TH in a pickup. They are most noticeable at light throttle, with mid-high throttle they aren’t as noticeable and the HO motor has the power to pull thru the earlier shifts.

The Aisin really doesn’t ever change temp as long as the torque converter is locked.

I agree, always assumed the C/C truck likely has some different programming. I do notice the difference in upshift points but it's not a big deal. If I'm in the throttle pretty deep, I can push the shift points out even with T/H off. Otherwise the shift point are at pretty low rpm's. Even the baby C can pull out of the hole though, it just pulls a lot better at higher rpm's. Little different than what I expected. I figured the Cummins would be a torque monster at low rpm's but it's actually kinda opposite. It thrives on rpm's.

View attachment 55225
If I have a trailer hooked to the truck, I run the in T/H. This is a 13,035 lbs parachute designed to destroy your mileage. When running one of these, I lock out 6th gear if it hunts. There have been many days that I get better mileage at 65 to 68 mph in 5th. T/H locks up the torque converter sooner to keep the fluid from heating up. The crisper shift aids in gaining speed when accelerating. The only thing I don’t like about it is when downshifting on steep grades it can get a little harsh, during slick conditions I’ll switch out of T/H and set the exhaust brake to always on. As far as the shift to 6th is concerned, it won’t do it until I’m done accelerating to speed. So sometimes it won’t shift until 70 mph but never before 60 mph.

That's not a parachute, it just feels like one! That's a boxcar on tires. LOL 7mpg all day.