If it's a new Tradesman you already have the small 17" rims and 265? Tires.
245s would gain you a shade, but not much.
First of all, you'll wet your pants after towing with the Cummins vs your 6.2. (2nd gear , 55mph screamin to make a hill in my 6.2 with a 14klb flatbed this morning!) so don't even drive it if you're not going to buy it! Lol.
Half the people will tell you you can't haul that much weight any way since the diesel is "so heavy", but you drop 2k pin plus load some weight in the bed and front of the camper you'll get the coils to squat a decent amount.
Cheap leveling kit up front will effectively drop the rear a little too.
After that you're kinda stuck without suspension mods to the truck or trailer of it's really that bad.