The GM 3500 vans are not available with AWD, only the 1500 series. However Quigley will convert the GMs.
You still have weight limit problems. GCWR = 16,000 pounds, curb weight = ~ 6500. Add in 1500 pounds of family and luggage, and you can only tow 8,000 pounds. Kind of the opposite problem of SUVs, because in this case you have plenty of payload, but not enough pull rating.
The GM 6.0 does make more HP, but quite a bit less torque, which means the HP for the GM 6.0 curve is less flat.
The 2500 version has less payload than the 3500, by about 1,000 pounds. It also comes with the 4.8L standard, the 6.0 is optional.
