Depending if you have an auto or not. With 5-speed you can still milk the mpg. If you are easy with the car and don't play alot with it your mpg's shouldn't change. I averaged 22mpg/tank with the 2.73s and now with 3.73s I still get 22mpg/tank. I get also get alittle better mpg in town but not quite as good on the highway but still can get mid 20's mpg at 70 mph. though my car is a bit lighter too which also helps. A 23 tooth speedometer gear ($15) corrected my speedo up to about 60-65 mph then it's a little off (by about 5 mph). You'll like the 3.73s. I had 3.55s in before the 3.73s and like the 3.73s a bit better. I do alot of driving too, highway and in town. Don't worry about the gas mileage. It's really not going to get hurt. Unless you play with the car alot.
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1996 Mustang GTS: 5-speed, K&N, removed air silencer, 3.73s, turndowns after stock H-pipe (no mufflers)
[This message has been edited by 96GTS (edited 06-30-2000).]