I am considering doing this to my car, but im concerned about my gas mileage, and my rpms at highway speeds. I was thinking either 3.73 or 4.10s. But my dad has made me leary of doing it because of the gas factor, and the rpms on the highway. I really would love to have a neck snapping take off. People that have done it, what is your expeirence with performance, gas, and highway rpms?