Very few people pay any attention to that. I dont, and am 100% sure I exceed that when towing rental travel trailers.
Its really a "cover your ***" for Ford. If your truck overheats when towing, they have a way to say "we told you so" and that includes using 91 octane when towing, which most seem not to heed that recommendation either.

 

Modern F-150s EASILY can double their rating on all counts. I would not worry at all if you are bumping up against the "tow rating".