Throw that 2,000 lb. plus (dry—not loaded) hitch weight for the fiver in the bed (plus a couple grandkids in the backseat) and we’re right on the brink (or overloaded)—unless I’m figuring this wrong. Assuming payload is calculated at the factory with a 150 lb. driver and 250 lbs of fuel, we can add 400 lbs. of payload back in, but that still leaves a LOT more leeway with the TT.
A TT hitch is about 100 pounds, a fifth wheel hitch is about 200-250 pounds. The hitch weight plus the pin weight almost requires a one ton truck for any large size fifth wheel.