Our new diesel hog truck has a gizmo that tells what your fuel mileage is at any given moment, apparently based on the current fuel flow. The difference between 55 mph and 75 mph (and before you jump on me, that is the max on interstates in AZ) is amazing. Takes a little longer to get from here to there, but at current diesel prices we feel that it is worth it. Besides, less stress, more time to enjoy the desert views, etc etc etc...