I've had the truck for two years and the gas mileage hasn't changed, but is 200 miles a tank normal? With a roughly 20 gal tank getting 200 miles that's and average of 10 mpg, that's just seems a bit low.... all the mods I have are flowmaster 40 series dropped off at muffler a K&N filter and 33 m/t tires.... regular oil changes and maintanance < can't spell sorry.