2016 Ram short bed 6.7 diesel 2500 payload close to max

The difference between the class 2 and class 3 is the GVWR, not the capability of the truck. The tire sticker is just the factory curb wt as delivered, minus the GVWR, which in this case, is for registration purpose.

Yes, if OP's tires are capable, adding air bags to springs will give same capability as 3500 class 3, which just uses a higher GVWR.

OP....look to your RAWR/tire max rating, rather than your payload sticker.

Jerry