Dually!! No choice
Diesel!! Not just for the torque, but for the diesel braking.
Consider moving up from a 350/3500 to 450/4500 or 550/5500. With a 350/3500 you will still need to consider Timbrins or something similar. I would skip the airbags. I tried those initially and had poor results. They made the sway worse and one broke after a few months of use.
Chevy, Ford or Ram will work. I lean towards the Ram primarily because of the CTD. Don't worry about DEF. It is a minor nuisance. You can find it everywhere for less than $15 for 2000 miles of driving.