attn: Weight Police

Adding springs and air bags doesn't change the GVWR, only the manufacturer can set that. Ignore it or don't, you should have known what it was before you bought it, but it's kind of late for that. Your truck is very heavy for what it is, being a loaded out crewcab just uses up a lot of the weight rating in actual truck. You are not alone - the early versions of the Dodge Ram 2500HD Mega-cab with the Cummins and 4wd could have a payload as low as 1200 lbs, less than almost any half-ton. Three-quarter ton class trucks can tow the heck out of things, but are often very poorly matched to fifth-wheels for just the reason that you've found - not enough payload for the pin weight.

Brian