With the Chevy/GM/Ram trucks there is no difference between the 2500 and 3500 trucks other than the number of rear leaf springs in the pack and whether you can get DRW on the truck as DRW available only with the 3500 models. When I bought my 2011 Chvey Duramax diesel 2500 pickup it was so I could get the standard length bed of 6'6" and the double or extended cab. With the 3500 I would have had to go with either the regular cab or the crew cab. Be careful as when I bought my Chevy 2500HD pickup with its 2800 lb payload capacity it had a higher payload rating than any of the SRW 3500 pickups on the dealer's lot. With Ford they have had more differences between their F-250 and F-350 models and so safest to go with one of their F-350 trucks if you decide on Ford.
I added a double leaf set of SuperSprings for $445 and an hour of my time to increase the payload from 2800 to more than 4000 lbs and I replaced the factory tires rated at 3095 lbs with new Nitto tires rated at 3750 lbs load capacity and I replaced the factory shocks with the Rancho XL adjustable shocks.
I drove the truck with the fully loaded Lance 845 camper and a total payload of 3700 lbs with zero issues and no problems with sway or handling of the truck and camper. It is very important to realize that in a turn there will be more than 50% of the camper load on one wheel and so on one tire and one set of leaf springs. If the load cannot be adequately supported then there will be sway and the shocks will be far less effective.
Truck frames were made much stronger on the 2011 and later GM pickups and on the 2014 and later Ram trucks and on the 2016 and later Ford pickups (which were the ones most likely to have a frame fail with a camper load). At least with the AAM axles used on the GM/Chevy trucks their load rating is 11,000 lbs so the payload is largely determined by the weight the leaf springs and the tires can support.
I highly recommend the Torklift frame mounted tie-downs and their FastGun adjustble turnbuckles (proper tensioning is critical as too much tension will literally pull the sides of the camper apart.
There are people selling their trucks with their campers and you will save more than $3000 or more in the costs of mating a camper to the truck properly. With a new truck there will the cost of the hold downs and the new shocks and tires and new wiring harness and battery relay and 20 hours or more of shop labor. Unless the model and year are known to have reliabilty or safety problems, which is easy to research, there is little to be gained with a brand new pickup.
With a new pickup plan on selling the tires on Craigslist and buying higher load capacity tires (Nitto, BF Goodrich, Toyo) and on replacing the shocks with the Rancho adjustable, and be sure that the pickup does not have one of the plastic drop in bed liners as this will make it more difficult to keep the camper from sliding in the bed. I gained 1310 lbs of load capacity at the rear axle with the new tires.
I went with the diesel truck for its power and ability to quickly accelerate and safely merge with freeway traffic and to be able to safely pass double trailer rigs going up steep grades and having the use of the engine exhaust brake when going down steep hills. I also got 30% more miles per gallon which meant that the range with the trucks 36-gal fuel tank was 30% greater. One cannot legally nor do aftermarket fuel tank makers have them to replace the factory gas tank. The front profile of the Lance camper produced a great deal of wind drag which impacted fuel economy considerably with a reduction of more than 30% even without a head or cross wind.
