I just barely bought my car i got an 07 grand prix and my gas mileage sucks as well. the only tip i have is that u fill up at night or early in the morning when its not so hot because the heat expands the gas therefore ur not getting the amount ur paying for. also, see what kind of gas u use because arco is crap i only put chevron premium in mine and my mpg is 24 now compared to 19.5