Yet another what can I tow question

Pretty sure you've got a typo, gross weight is probably 5,178 pounds which would give you a payload of just over 1,800 pounds. Combine that info with the max tongue weight and the max trailer weight and all your numbers agree as doing as your occupants and stuff in the bed weigh less than 600 pounds. If they exceed that then reduce the max trailer weight by 7 pounds for every one pound over.

However, that's theoretical maximum, conventional wisdom is you won't be very happy over ~30 feet or 6,000 pounds unloaded if you average what most around here who have been there say.