Found these links on another site that says if you add acetone in small quantities (like 3 oz per 10 gallons), it will add about 2-3 mpg for Hummers.
http://pesn.com/2005/03/17/6900069_Acetone/
http://peswiki.com/index.php/Directo..._Fuel_Additive
Anyone here willing to try this?