I tow a 6.5-7k trailer with mine all over the Southern Sierra (out of Fresno) without too much issue. Our grades are a lot steeper down here. It does get a little nerve racking on long downhills as the Ecoboost has very little engine braking. I downshift it and let it rev. 4,000-5,000rpm seems to provide the most engine braking. Always make sure my trailer brakes are up to snuff and have fresh brake fluid in the truck.

Mine likes to overheat on long grades when the ambient temps are above 85F (already had many discussion on this forum about it). Coolant and tranny. Typically have to pull over halfway up. Going to try a larger tranny cooler this year and see if it helps.