GVWR on 2500HD trucks is limited to the delta between 10,000lbs (general class 2 truck rating) and the weight of the truck, which is 7-8000lbs depending on model. Take a extended cab gasser 2wd, rated payload may be 3000lbs. Same chassis, 4x4, crewcab loaded diesel, payload will be more like 2000lbs.......to saty under the 10k class 2 limit.
Additionally mfgs either add in some additional cargo assumed in the truck before figuring the truck camper rating, or reduce the recommended payload due to the high and rearward CoG of a TC.
Either way, any newer 2500HD, has ample rating to put around 3klbs in the bed with minimal modifications to the truck. Same axle, chassis and drivetrain as 3500s. Lighter spring rate and the 10klb class gvw restriction are typically the differences.
If you're really sticking with a lighter camper (under 3klb ready to roll), don't scare yourself out of a 2500....unless you want to. 3500s have their virtues too.