Duramax Performance while Towing

[DMaxPiston]

This past weekend brought home 5th wheel (approx. 10k lbs empty) with our fairly new LBZ duramax engine. Put it in drive (not optional M) and used the trailer/tow mode. It seemed to me that the shifting point was high. It would shift gear right around 2400 RPM. Therefore, at times, I was running at 50 MPH and 2000 RPM, and if my memory serves me right it was in 4th gear. If I was driving manual trans, I probably would have shifted up. Is this normal? What have others seen? What should I expect of the engine. Look for others experience.

[Inspector]

In T/H mode the shift points are at a higher RPM. My 5 speed will not go to OD until 55mph or a bit higher depending on terrain while towing in T/H. I'll bet your 6 speed acts the same as mine. You'll have to ask those who have towed with the 6 speed if they can tow in 6th. Chances are it stays in 5th most of the time while towing heavy.
Denny

[OC_DMAX]

I tow an 11K pound 5th wheel. With a speed limit of 55 mph (here in CA) when towing a trailer, I try to stay between 55 and 62 mph. With the tow/haul function engaged, the truck will stay in 4th gear up to around 60 mph. Usually, I disengage Tow/Haul while cruising the level highway. It up-shifts to 5th gear around 55 mph that way. Otherwise, I would experience the same frustrations (engine reving needlessly).

[BozDMAX]

14K+ fifth wheel and I have the same experience as OC. My shift point to OD happens right about 57mph if I am not pushing it to go faster. It will stay in OD until the speed drops to 54mph or so on a rise. That is also just about the speed for the best mileage. On the flats, I will leave it out of T/H mode.