2021 3500 SO transmission shifts during towing

[Yeasty McFlaps]

Hi all, so I towed with my ram 3500 6.7 for the first time. About 8000 lbs, and 7 hours round trip. With tow/haul engaged, in cruise control, as I headed up hills At 60 mph, the trans would shift out of sixth (1200 rpm), then it would rev to 2500 rpm, finally settling down to 1700 rpm, fifth gear. It did this consistently for the whole trip. Why wouldn't it simply shift into fifth? Why the big rev? Anyone else experience this? Thanks in advance.

 

[Brutal_HO]

Sounds like normal TC lockup, perhaps a bit much on the flare but I drive an HO that's different so I can't say for sure.

1200 is pretty low RPM to pull a hill in 6th. If you're going to run @60MPH, I'd just lock out 6th gear and let it cruise @1700RPM with a locked TC and not have it shuttle shifting. Peak power and efficiency is like 1900-2000.

Remember these are tightly emissioned vehicles so they're not going to want to lug down low wasting unburnt fuel.

 

[Yeasty McFlaps]

Sounds like normal TC lockup, perhaps a bit much on the flare but I drive an HO that's different so I can't say for sure.

1200 is pretty low RPM to pull a hill in 6th. If you're going to run @60MPH, I'd just lock out 6th gear and let it cruise @1700RPM with a locked TC and not have it shuttle shifting. Peak power and efficiency is like 1900-2000.

Remember these are tightly emissioned vehicles so they're not going to want to lug down low wasting unburnt fuel.

Copy that. Thanks I'll do that. It's unfortunate, my ecodiesel shifted better than this truck. And cost half.

 

[jkempken]

Mine does the same thing, 2020 SO 3500

 

[Brutal_HO]

Copy that. Thanks I'll do that. It's unfortunate, my ecodiesel shifted better than this truck. And cost half.

Towed 1/4?

 

[Yeasty McFlaps]

Towed 1/4?

Ecodiesel towed 8800 lbs. Which was ok for most stuff. The problem with the ecodiesel: nobody works on them. Also payload was 1300lbs! Which is an empty truck, an RV and a family! Also there's the whole ticking time bomb thing.... egr, etc.

 

[Yeasty McFlaps]

But big picture: why can't ram tune the engine to defuel instead of revving way up to 2500 rpm? Why does it overshoot? Is there some engineering reason to rev up from 1200 to 2500, then back down to 1700 to finally find its gear? Dumb iron

 

[H3LZSN1P3R]

But big picture: why can't ram tune the engine to defuel instead of revving way up to 2500 rpm? Why does it overshoot? Is there some engineering reason to rev up from 1200 to 2500, then back down to 1700 to finally find its gear? Dumb iron

Its the converter unlocking in 5th then locking up thats normal and helps extend the trans life by upping the shift pressures

 

[TombJJ]

I noticed mine (2021 2500 Tradesman SO) towing last week with 7K would do the same. I just locked it in 5th for the big hills and let it cruise up. I didn’t think of the shift pressures.

 

[1FstGPa]

My 68RFE is great at down or up shifting pulling no load. That all changes when I slap on 10.000#. Upshifting is fine, but downshifting it slides a little too much to make me happy. I never mind the little bump when changing gears and I never considered manually shifting down since the trans is an automatic (in theory).

A little story:

I have a buddy back in AZ that has the same driveline setup as mine. His 68RFE shifts with a little authority. No kit and I believe no tune (need to ask him). The only difference between our 2500s is his has over 100,000 miles and mine just turned 4000 miles (still breaking in? Eh?).

So! My local-out-of-town stealership (that's what you get when you live in a small mountain town) is pestering me with emails to bring the truck in for it's "4 month service." Meh! When I have time, next week or so, to let them do their thing, I plan on asking them about changing the shift pressure to acquire a little firmer shift. Of course, I already know their answer, but it never hurts to ask...Right?