This is a question about the trans. Should I just leave the truck in "D" and go or should I be in manual mode and restrict it to 5th gear? The truck seems to be laboring on slight uphill grades but will pull no problem if you mash it to get it to downshift. The truck is a 2008 with the 6 speed Allison.

Leave it in "D" and select "Tow-Haul".Your computer is smart enough to figure out the best gear to be in.

kaydeejay wrote:Leave it in "D" and select "Tow-Haul".Your computer is smart enough to figure out the best gear to be in.Yep, I agree too. Leave it in D.The only time I need to shift up or down is going down or up steep grades but even then it's rare I need to fiddle with anything.

My Allison doesn't have a tow haul mode so I will drop it down gear by gear depending on how steep and long the grade is. I pull a 15000 lb 5th wheel and on 6% grades I'm often in second gear under 30MPH with the go pedal pushed to the floor. This seems to be a good place for the engine/trans, very smooth, no lugging and temps don't climb up.

Leave it in D and use the tow haul mode. I pull a 14600 lb fifth wheel with the cruise set at 62 and let the truck do what it does best, pull. The only time I turn the tow haul mode off is if I'm going down a hill and then need to shoot back up another one. In tow haul with cruise on she'll down shift to keep speed. Just let your truck work, she's a towing beast.

On the freeway and close to flat ground, just put it in Drive. In town, always tow/haul. Mountains, or anywhere it is hunting for a gear, tow/haul.

Duramax and towing a 10600lb 5th wheel | Good Sam Community

the_bear_II
Explorer
Jun 01, 2015
My Allison doesn't have a tow haul mode so I will drop it down gear by gear depending on how steep and long the grade is. I pull a 15000 lb 5th wheel and on 6% grades I'm often in second gear under 30MPH with the go pedal pushed to the floor. This seems to be a good place for the engine/trans, very smooth, no lugging and temps don't climb up.
Frostbitte
Explorer
Jun 01, 2015
kaydeejay wrote:
Leave it in "D" and select "Tow-Haul".
Your computer is smart enough to figure out the best gear to be in.

Yep, I agree too. Leave it in D.
The only time I need to shift up or down is going down or up steep grades but even then it's rare I need to fiddle with anything.
kaydeejay
Explorer
Jun 01, 2015
Leave it in "D" and select "Tow-Haul".
Your computer is smart enough to figure out the best gear to be in.

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Duramax and towing a 10600lb 5th wheel

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