Are you running stock tires and wheels as well? Extra weight knocks that MPG down quite a bit. Buddy of mine has a 2.7 that we took on a hunting trip and it was getting nearly 26 MPG on the highway completely stock.2017 Ford F150 2.7 Ecoboost (crew cab, short box, topper) stock suspension.
Everyday == 19-20ish
Highway 70mph or less = 22
Interstate 80mph = 18-19
I'm truly disappointed in the mileage compared to many of the other Ecoboost trucks posted and wish I would have purchased the 5.0 or 3.5.