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8th gear - highway speed?

pizzatots said:
New truck. 6.4 with 3.73s. Noticing at 65mph the truck stays in 7th gear. If I bump up to 70 it will fall down to 8th gear. What speed does this truck like to go in to 8th? Anyone notice?
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I played with this on my '24 yesterday. Seems to stay in 7th until I get to about 69 mph then it bumps to 8th.
 
My truck seems to catch 8th right around that 67 to 69 mph speed, but won't downshift to 7th even if speed reduces to just over 60, it'll just cruise right along until there is a hill or throttle is needed to pass some other vehicle.
 
Most of my driving is in town, so I rarely get above 6th
 
Firebird said:
Most of my driving is in town, so I rarely get above 6th
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22 years ago I was regularly driving from Southern New Jersey to South Carolina and back on rt95 in a Jeep Tj. Good old three spd auto. No overdrive. Boy have things changed!
 
My 6.4 2500 with 4.10 gears will shift into 8th gear around 50 to 55. Today driving empty going up a slight grade it held 8th while still doing down to 54 mph as slow as I was willing to go.
 
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pizzatots said:
Someone posted this to another forum for the ZF, and it really jives with what I'm seeing. Shift to 8th with the 3.73s comes around 68-69mph, since that is around 2k RPM in 7th gear.

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Do you know if this is the same for 2024, 8 speed in 2500 4x4?
Still trying to figure it out after trading in my 1500 rear wheel drive.
To me it feels like it is waiting too long to shift into 7th, 8th gears and am not sure why it waits other than truck is heavier than 1500 and built to pull more than cruise.
I can get shift at moderate acceleration between 60-65 but 8th seems to hang and does not shift anything like the 1500.
I've got the 3.73 in this one, the 1500 had the 3.55.
Still running stock wheels which I believe are either 8 or nine inch x 20 and 285/60/20 tires.
Hate the look of the tires under the wells, will be moving to 35x12.5 soon if I can find someone to sell the 285/60 set to.
*Watching the rpm vs mileage vs shift currently as I only have 500 miles on the truck. Will be interesting to see if this changes as things loosen a bit. Some report that mileage improves a bit as does noticeable drag on the truck.
Been a while since I've owned a 4wd so I'm also thinking I'm feeling the 4wd drag compared to the ultra-smooth acceleration/cruising of the 5.7 in 2WD in the 1500,.
Just put the Flowmaster FX dual outs on the truck. Sounds really nice now compared to stock single.
Putting the AFe intake on next week to get the basic's back to all my past trucks.
Only thing I really don't like is the inability to lower the 4x4.
Don't want a low rider but I wish there was an easy option to get the truck down to the height of the 1500 without significant modifications and compromise.
 
I don't think there is any noticeable 4WD "drag" on any of these trucks, as compared to 2WD. I think you may just be feeling the added heft of the 2500, I notice when I drive a 1500 that it feels lighter and more nimble, which makes sense. And if you prefer a lower stance why put the 35's on, depending on brand they will add about 1/2" or a little more to truck height?

AFE intake won't do anything for these trucks, stock intake performs well.

As for shifting, maybe as it learns a bit more it will drop into 8th sooner, I agree 68 seems a bit much.
 
ollicat said:
Sorry, where are you seeing what gear you are in?
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If in drive, and not selecting a gear with the manual gear select, you won't see it. But you can easily feel the 7th-8th-7th shift and watching the tach you'll see the rpm drop. The way these are geared, you wouldn't be able to miss being in 6th on the highway, will likely be up near 3000 rpm and roaring, so the drop to 7th is easy to see and then wait for the drop to 8th when there's enough speed and not much load (level ground). Hope that makes sense.
 
You could also use AlfaOBD or JScan to enable the gear indicator.
 
Coming off a 1500 Rebel with 3.92’s. Wonder what the logic is to keep the 2500 running a lower gear and higher RPM at lower speeds ? I spend a lot of time between 50-60 mph in 7th gear, 1800 rpm, if a caught 8th I would be less than 1500 rpm which too me would be better fuel econ. Almost like your in tow/haul mode all the time. 6.4 torque could pull 8th at 50-55mph. Wish it would shift into a higher gear sooner for my driving and get better fuel economy.
 
DIRTRIDER said:
Coming off a 1500 Rebel with 3.92’s. Wonder what the logic is to keep the 2500 running a lower gear and higher RPM at lower speeds ? I spend a lot of time between 50-60 mph in 7th gear, 1800 rpm, if a caught 8th I would be less than 1500 rpm which too me would be better fuel econ. Almost like your in tow/haul mode all the time. 6.4 torque could pull 8th at 50-55mph. Wish it would shift into a higher gear sooner for my driving and get better fuel economy.
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The HDs are pushing a lot more weight and wind than the 1500s. If they shifted into 8th that low you’d end up with them hunting gears a lot.
 
My 2021 would shift into 8th around 55-56 if I wasn’t accelerating to vigorously. My 2024 hasn’t seen 8th gear yet………..it’s definitely different but to be fair, I haven’t eclipsed 100 miles yet either.
 
DIRTRIDER said:
Coming off a 1500 Rebel with 3.92’s. Wonder what the logic is to keep the 2500 running a lower gear and higher RPM at lower speeds ? I spend a lot of time between 50-60 mph in 7th gear, 1800 rpm, if a caught 8th I would be less than 1500 rpm which too me would be better fuel econ. Almost like your in tow/haul mode all the time. 6.4 torque could pull 8th at 50-55mph. Wish it would shift into a higher gear sooner for my driving and get better fuel economy.
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Fuel economy isn't linear with low rpms like you might think, my guess is the 6.4 running 1500 rpm in 8th vs. 1800 rpm in 7th has nearly identical fuel burn. If the truck was loud I might wish it shifted into 8th sooner, but it's such a quiet ride that it doesn't bother me at all.
 
Finally saw 8th gear today, shifted somewhere around 68-70. As @Dave01 alluded to, turning 2k in 7th is usually better than 1600 in 8th. I’ve found at elevated speeds I get better economy around 2k, anything less and the motor lugs a little which kills economy from fuel loading.
 
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