When my car was N/A with stock gears I was getting around 23 mpg highway. I installed the 4.10's and dropped to around 20mpg highway. I now have a Saleen S/C in the car and can't for the life of me get better than 18mpg highway. I don't drive 55 and would not be able to even if it gave me 100mpg. This is my 3rd vehicle but I still put 10,000 miles a year on it.
If you're going to drive it like a P***y to get better mileage don't bother getting one cause you'll be very disappointed. These cars put a smile on your face with power and not creature comforts and refined handling. (Putting flame retardent suit on as we speak)
05 White GT Premium 5 Sp. IUP, Active Alarm
BMR, C&L, Centerforce, Fidanza, FRPP, GI Joe, JBA, JDM Engineering, LPW, Saleen, SCT, Steeda, SOS
S/C 1.613 60'. 4.748 330', 7.332 @ 93.75mph 1/8th, 9.566 1000', 11.427 @ 119.92 1/4mile