I suggest you look at the sticker on driver's side door column as it will tell you the payload capacity. Having said that my 05 Ford PSD super cab had a payload capacity of 2736 lbs. Our 29 ft 10k fiver took us within 50 lbs of its capacity. I figured I could go as high as 13k lbs without exceeding the RAWR or GCWR, however there was just the two of us which helped with payload.
In addition don't believe Ford's 5th wheel towing capacity numbers as mine was rated for just over 16K lbs which was an unachievable number.