Alright background first i have a LT4 in my camaro with a six speed. I put the rear end out of a forth gen with disc brakes in and it has like 2.73 gears. The computer was programmed by the guy i bought the engine from and used a hypertech programmer. I am having it set back to stock so i can see what kind of gas mileage i can get out of the car right now i get i estimate about 12 miles to the gallon out of it and that is high way.... imagine my dismay when i figured i should be recieving a bit more. I have an adjustable fuel regulator but i still can not seem to beat the gas mileage i have set it as low as 35 psi as high as 75 and still the same result. i put it at 40 right now. Is the ratio i have for the rear end causing a problem would 3.42 help. would this work better with the six speed. any help or suggestions would be greatful.

Something seems very wrong. An LT4 in that installation should be getting well over 20 MPG highway mileage, even under a relatively heavy foot.