Tire type makes a big difference. With highway tires my van will get 21 mpg at 65. With M&S (Revo's) the best I can get is 17. Of course the van will now actually stop in the rain - mighty handy at stop signs.
Using your GPS doesn't give you more miles per gallon, but it can still save a lot of fuel. If your GPS has the ability, let it plot out the most efficient routes for you. My GPS almost always finds shorter routes than I would have used, especially around town. In a ten mile trip all you...