My car was a 25+ car also with the GT-40 heads and intake, B-cam, and other bolts ons. However, it has dropped off recently and I can't figure out why
. I don't think my engine is getting tired or anything. I may have a bad sensor or something.
You can get pretty good mileage even with some add-ons to your car, although as stated before, city driving seems to always be poor.