Have been wondering for some time now about the gas mileage on my classic. Using the Vance & Hines slip-ons, and a V&H fuel pak. I got aggraviated one day, & unhooked the fuel-pak. Gas mileage went back up to 48 mpg. Got to worring about doing harm to the engine, and hooked it back up. Rechecked, and am only getting around 38mpg. Called V&H today,about the difference in mpg. He asked me about the bike, and said that was about average on the mpg. I dont think I would recommend a V&H fuel pak. Glider, do you think a different programmer would raise the mpg back up. Hate to go back to the stock exhaust.