What rear end gear ratio do you have?Hey Welcome! You should see a increase of a couple of MPG in comparison (loaded/towing). The EcoBoost has massive low end TQ and will get the trailer moving fast with less effort. That will be the big difference you noticed next to the fact that it will lug the two overdrive gears all day long (5th and 6th gear) when towing saving on the fuel.
I have the taller 3.73 rear end and often tow either a 27' enclosed trailer (V-Nose), 18' enclosed trailer (Flat nose) and/or a 20' flat deck and the weight ranged from 8,000lbs to 11,000lbs and I average low-mid teens in the two enclosed trailers (8,000lbs or less) and with flat deck (11,000lbs) about 9.5mpg to 11mpg (speed 60-70mph). Granted in Alaska there are not many flat roads and towing is up and over hills and thru long twisty passes. The folks with 3.31 and 3.55 rear ends still do just as well and often better on MPG, especially empty and down on the real highways!