I was going to say, holy smokes, my 05 GMC gets 12 to 13 towing a 2 place with salt shield. I certainly thought the eco boost would get better than that.I have over 8,000 miles on my EcoBoost and have about 2,000 miles pulling my enclosed 23' inline trailer with one sled. The engine pulls similar to the diesels I have had. As some have noted, it is lighter than a diesel and can float a little. As for mileage, I got 9mpg pulling and not much better than 15mpg on the open road.
I love the truck, but I am disappointed with the mileage. My Excursion 6.0 would get 14mpg pulling (and you never knew anything was behind you) and up to 22mpg on the open road.
If you go to the F150 forum you can read up on both sides of the opinion and mileage results. Some folks are seeing much higher mileage than I am. My son also bought a F150, but went with the 3.55 rear end and a 5.0. He gets over 20mpg on the open road but he has never towed.
As others have said, if you test it you will go home with one.