Also, how good are you at keeping your foot out of it? It sounds like there's a good amount of power-adders here. Are you good at leaving that power on the table, or is your right foot a little heavy? Try driving for a week straight as if there was an egg between your foot and the gas pedal. I did it once when I daily drove my valiant with the 318 mentioned above. Jumped from 11-12 mpg to 16 mpg, changing nothing else.