There's more to this than just make of vehicle ! You have to consider weight , trans gearing , rear diff gears , and motor size . Hills , even tires make a difference . Are you towing anything ? Is your rig shaped nicely to cut into the wind , or is it an old box shape , preventing any decent drag co efficient ? If you can research a little, you can beat the odds just by first getting these points in your favor , and then drive without a lead foot , you might realize decent gas mileage . example : a 360 Dodge properly geared will allways beat a 318 that is forced to turn 3000 rpm's at 60 miles an hour . If you can keep the rpm's down , you win in the heat + wear department as well !