I have an '05 2WD drive 3500 dually with 108,000 miles on it. I pull a 45' hot shot trailer out of Henderson NV. My average gross weight is 28,000 lbs, up and down mountains and across the desert. I have yet to put a wrench on the D-Max or the Allison, other than oil and complete filter changes at 10,000 miles.
The truck gets a little over 8 mpg loaded...who cares when you make an average of $1.20 a mile on the low side loaded and empty!
The only thing I'd trade my 3500 Chevy for is a 4500 Chevy!
Jerry