well right now i have 373 and 33, i get 11 around town and about 12.5 on the highway. Averaging 75 mph. I have a set of 456 waiting to be put in and i was just wondering if you guys think that will help or kill my mpg. Im thinking that it will turn more rpm's on the highway but the vacuum will be lower since it wont take as much gas to maintain that speed. let me know what you guys think.