The 2500 truck will have leaf springs that support less weight than those on the 3500 SRW truck which will have less than that of the DRW version of the 3500 truck.
The factory calculates the GAWR based on how the truck is configured when it leaves the factory and based upon the weakest component. For most trucks it is the leaf springs followed by the tires and rims. Both can be upgraded for the purpose of carrying a greater payload.
Easiest way to retain the handling of the truck and increase the payload is with Supersprings that take an hour to install and will outlast the truck. They work just like the factory overload leaf pack that is installed at the factory on the 3500 trucks.
Air bags are good when you need to be able to adjust the rear height of the bed for towing a 5th wheel trailer.