I'm averaging 17.5 for the life of the car...right now around 16.7 on this tank lol

 

I think it depends on terrain, conditions, city v. highway, etc. If you can start off in second gear and shift to fourth then to sixth you get better mileage. I prefer the performance, so I start in second and work my way through. Shift points are around 3000 RPM. I have been as low as 14.8 MPG in the city and as high as 25.8 on the highway. However, I recorded what was average for me. If you think there is something amiss, check your fuel to air ratio...it should read on average 14. Other than that, you could have Ford check it out or go to a performance tune place. I did see an increase with the CAI and 91 Octane performance tune of 1 MPG on average.

 

2014 GT Track Pack, Steeda CAI and Tune. 14.8mpg is a blessing. I usually see 11.5mpg around town. Best I could do on highway over a 150mile trip was 23.4 but that was driving it like a Prius. The ride back was 18.9mpg and a lot more fun. One of the lucky ones I guess. My job pays for my gas.

 

In addition to my Mustangs, I own a Camry Hybrid. That car gets on average 38 MPG. The all time best mileage was 43.3 MPG on a 600 mile road trip between Kansas City to Paragould, Arkansas. Try as I might, and as much as I enjoy great gas mileage, this car is never fun to drive. Comfortable yes, fun no!

 

There are 3 more gears above 3rd ;-)). Just kidding, but if you have a lot of stop and go, that kills gas mileage.

 

2014 GT 6 speed 3.73-90% highway miles in the 70-80 mph range, I average just under 23 mpg. I commute 130-sh miles per day. Bought the car in Feb and have 25,000 miles on her.