OP, I have a '10 F150 5.0 and tow a TT that weighs about 5200 lbs empty and can carry 7000 lbs loaded. I have not added airbags or leaf springs, just careful to stay under my payload (per sticker on truck). The thing that I have to pay most attention to is the tires. My truck came with P265 tires on it and they are just too soft without some extra air. Sticker recommends 35PSI, but I have found for towing bumping the pressure up to about 40 makes it feel less squirmy in the back. When I buy new tires (next year), I will probably buy a different load rating and get some with a stiffer sidewall. Just gotta decide if the amount of towing I do justifies the stiffer ride I will have all the time.