GM gives that year model truck a 9350?? rawr for carrying weight in the bed. These trucks rear axle may weigh in the 3400 lb range for approx 6000 lb in the bed payload.
You have the truck so drop by your local CAT scales at a truck stop and get your trucks separate front and rear axle weights with close attention to rear axle weights as its carrying just about all the TC.....That way you know how much truck camper your particular 3500 DRW can carry.
I wouldn't do a thing to the truck before adding a truck camper and make a short local trip. Then is the time to decide if suspension help is needed.
