Hi All,
New duramax owner here and so far I am very impressed with the new ride. I have a quick question. I am pulling a 7500 lb boat to my local ramp (approx 50 miles.) My question is for this load should I be using the tow haul mode or not? The tow is mostly level ground with a few small hills. Thanks for any help in advance.

As a general rule we do not use tow/haul with a load under 8000 pounds. I think the dealer told me this in 2001 when I bought my first Duramax. I have not seen or heard anything different since. I would lower it to 6000 pounds if you have a chip, just to be on the safe side.

I don't like the fact that the Allison in Tow/Haul mode can downshift three gears in a long downhill situation- I don't like seeing my diesel over about 2500 rpm for any long distance. In normal mode, it will only downshift one gear. If I was in a long uphill situation, I might use T/H for the extended shift points, but I'd still be watching the tach.

I turn it on or off depending on what I want the truck to do. If the transmission downshifted climbing a hill and doesn't want to go back up to fifth, I will turn it off and then back on after the shift. If I am in conditions that require the use of first, second ,or third gears, I keep it on to keep the torque converter locked and lower the transmission temps.
gozierdt: Why do you want to keep the rpm so low. Red line under power is 3200 RPM and 4800 RPM for grade braking when not applying power. The computer will not allow you to over-rev the engine. I always want to use the grade braking feature before riding the brake pedal.

Right On Dave,

Idahofox

I always run Tow/Haul mode when pulling a trailer (5th Wheel and a boat). I do this mainly to take advantage of the torque converter locking up in gears 2 through 5. During the summer months, this helps in keeping the tranny temps in check (especially off the highway). If one were just running down a level highway, tow/haul may not be necessary.