Exact configuration of your truck can make a difference. Wheelbase? Axle ratios? Tow/payload packages?
According to Ford's towing selector book for my year F-150, the only thing holding me back to a max of 9200 lbs. is the 3.31 axle ratio. If everything else was the same, but it had come with 3.55 or 3.73 gears, the max would have been 11,000 lbs.
Keep in mind the 80% rule too. You wouldn't want to regularly use more than 80% of your max towing limit, which in my case, limits me to 7360. Still some nice campers you can find under that limit.