Ford Tow GuidesLooking at the 2002 F250 (it has a 7.3 but I don't know what year you have) GVWR is 8,800# and cargo capacity is varies from 4x4 Crew cab of 816# to 4x2 regular cab of 2,319#. Most configurations are around 1,400# of cargo capacity. Cargo capacity includes the weight of you (if over 150#), passengers, fuel and anything else you put in the truck.
Since the 5th wheel run 15-25% pin weight (in bed of truck), averages around 20% pin weight (mines 22%)a 12,000# 5er will have a 2,400# pin weight.
Don't look at dry weights as no one pulls an empty trailer. My dry weight is around 10,500# but when loaded we are about 12,000#. Max on my 5er is around 14,000#
Starting around 2005 the tow/cargo capacities of the trucks took off. You will notice in the rating prior to 2005 that 20,000# GCVWR is the max. You can add features but the rating just stops. In 2005 that changed.
With that truck a TT might be a better option for you.
Good luck.