Your mpg sounds a bit low. Not many miles, so that's weird. Do you get on the gas pedal a lot? Even so, that's too low.
Maybe a tune-up, clean your MAF and PCV, or check to make sure your using the proper octane for gas. No use using 91, if 87 will do. Not sure about octane for the Cobra, though.
A free tip is to check your tire pressure every 1-2 weeks as that will make a minor improvement along with making sure your alignment is good. Of course, this is good for optimal tire wear.
I'll be lucky to get 13mpg in city&highway conditions. A little more with just highway. Plus my car is alawys tuned up, unless I am just missing something?
Ford rated us at 17 city and 25 Hwy. I get 17 with strictly city driving, 18-19 with a little hwy trip in the mix. I'd prolly get every bit of 25 with a long trip of all hwy on a full tank of gas.