Dang Good

I have a 2010 F-150 Crew Cab with a 5.4 motor, 4x4, and towing package. The truck can haul 9500#. I am looking for a 5th wheel camper. Two people stated if I get anything over 6500# I will "pull the guts" out of the truck. What gives? Is there a special design needed to haul 9500#? Thanks,