Hmm must be a really small 5th wheel for a non HDPP F-150 to be able to tow it. Max 5th wheel GVWR for the 1500 is 9500 pounds. Even at just 15% Pin, that is 1425 pounds pin, plus 200 for the average hitch, 1625 pounds, but I doubt it can even come close to 15%, more like 18-20%. Are you sure you have 2100 pounds payload, or just ignore GVWR, FGAWR, and RGAWR?
Other than the HDPP, and I have reservations on even that, just because it say's it could, doesn't really mean it should.