I have a stock Duratec and I usually get about 25 miles to the gallon in mixed driving and about 30 when its all highway. Like the other poster said, when people add mods they do tend to drive harder, perhaps subconsciously but it is usually true.
When I first got my Mystique I would floor it when the light turned green because the acceleration felt so good. My gas mileage was awful (about 19-20) until I stopped doing that. So making some changes in your driving habits might help.
Also, make sure you are up to date on all your maintainance, especially air/fuel filters and such because those things can make a difference.
