I haven't towed my new TT enough yet to have a feel for what I'll get, but it will probably be pretty similar to what I see posted usually 8-10 mpg for an F-150 EB.
For daily driving, I get 18-19, on the highway alone it goes 19-20. It's sort of ironic - back in 1967 I bought a '63 Impala 4d HT with 300 hp 327 and it got around 18 mpg. In 1982 I bought a 1980 Toyota 4x4 std cab pickup - it got 17 mpg out of a 4 banger. Now my shiny new 2016 F-150 3.5L EB 4x4 gets mileage in the same general range, but.....
....the f-150 it gets that mileage in much better style with more usable power than anything I've ever owned. The Toyota was scads of fun for 4-wheeling, but bogged down on a lot of hills to as low as 40 mph on the highway. Now I can keep my normal speed on those same hills even when towing. :C