I use my F150 3.5 Ecoboost to tow a 7500 lb trailer. No issues though I would not pull anything heavier than that. Aside from the all-terrain nitto tires, rear sway bar and WDH, my truck has no other mods.
I went with Air Lift from 4wheelonline and put the savings towards a weight-distribution hitch. The Air Lift bags really help out supporting the weight of our trailer.