Anyone ever experiment with mpg's using different brands of fuel. I work with a cummins guy who swears some are better than others in his and it is enough of a difference that it is worth the extra cost vs. the cheap fuels. I've been using walmarts murphy in both of mine and don't seem to get as good as many on here claim they are getting. I'm thinking its time for me to experiment with different brands just to see if I can improve mpg's. I just wanted some input from anyone that has noticed a difference in the brands.