zr800 -- Assuming your truck was empty, your curb weight of 6500 lb must be incorrect. Looking through the factory specs for the 2004 F150 (available on this website), curb weights of empty trucks ranged from 4788 lbs for a regular cab short box 4x2 configuration to 5502 lbs for the 4x4 SuperCrew. Better go back and check that 6500 curb weight figure. I'm sure you will find that you have more payload capacity than you fear.