Just came back from another trip with my 2014 ecoboost F150, towing 4500# loaded, Amerilite, with 3:15 axle in the hills of central FL.
Couldn't have asked for a better match.
Towed W/towhaul on at all times. It could pull some pretty good hills(not mountains) without shifting, at 1500 rpm.
Only have about 2000 miles towing on it so far, but I love it.
Got 11.5 to 12.5 towing in the hills of Buckhead ridge, the only decent hills near here, and about 11.5 average HWY at 65.
I would have no hesitation pulling a loaded TT of 6500 to 7000 with this combo. Beyond that I would probably want a lower ratio, but until I go over that, why buy extra gas?