I've had my EAT chip for years now. When I first got it my mileage improved by about 1-2 mpg city. Just make sure you don't offset the mpg gain by sticking your foot in it more often because you will 'feel' an increase in performance (although our wagons are still dogs....). And it does seem to need premium grade, knocks pretty bad when I've tried regular. But you say your only getting 17mpg now? Sounds like you might have other problems. I get 23 city, 28-30 highway. You have the stock M50tu?