Before you do ANYTHING else, pull out your owners manual and read it. It should tell you somewhere in there what the towing capacity of your truck is. And not all F150's are the same, so don't let anyone tell you "Oh, an F-150 can pull XXXX lbs." My 2009 Silverado manual lists 99 (NINTEY NINE!!) different towing capacities ranging from 4,400 lbs to 13,000 lbs, depending on cab, engine, rear end gearing, transmission, cooling packages, towing packages, etc.
Looking here http://www.motorcraftservice.com/pub.../10f12og3e.pdf
I looked at your owners manual and it lists 62 permutations ranging from 5100 lbs to 11,300 lbs.