I had a 2006 F-250, 6.0 MAYPOP Powerstroke, extended cab, short body, 4X4, SRW, 35 gal aux fuel tank and tool box. In 2012 I bought a heavy 32 foot gooseneck hitch Cargo Express enclosed car trailer and loaded my 5000 lb 1949 Diamond T 1 ton pick up in it. I was grossing right on 21,000 lbs with 5500 lb on the drive axle. I was legal as far as axle and tire capacity. Then I added the Firestone air bag helper springs. They helped BUT even though I was legal I was still not comfortable.
This past July I swapped for my 3500 Quad cab, 6.7 Cummins, Aisin, DRW, 2wd, C&C with a built in hitch flat bed, and 60 gal aux fuel. I am now grossing 22,500, full (110 gal) of fuel, with no passengers or luggage resulting in 7260 lb drive weight. VERY comfortable, handles like a dream. Towed from Greenville SC to Winchester VA and back running 65-68 MPH up and down the hills of I-77 and I-81 and barely knew the trailer was behind me..
I definately recommend that you stop at a nearby truck stop that has a CAT scale (big yellow and black sign). Watch where you stop on it as these scales are set up to give you individual weights for steering, drive, and trailer axles as well as a gross weight. The best $10 you ever spent and if you move your load in the trailer around you can go back within 24 hr with your original ticket and reweigh for just $1.
Trailer not hooked just backed under