I pull with an '02 2500HD. D/A Extended Cab/Shot Bed.
Love it!
I've installed an Edge Products Inc. "Hot Juice Box"
which gives me an additional 125HP at the rear wheels.
Torque is approximately 250Ft. Lbs. over stock.
I have four choices of power levels,60,75,90,&125.
When pulling in the suggested 60hp level in tow haul mode
the truck very seldom will downshift.
You'll still get the mileage and will give your Duramax a great power increase.
I really enjoy driving my truck "Juiced"