The problem with the MPH vs MPG thing is that the logical endpoint is the old Soviet Express Card...Don't Leave Home. Fuel burn is minimized at zero speed.
But what is your personal time worth to you?
2000 Ford F-350 Super Cab Pickup
4x2, 6 speed manual
Regeared to 3.08:1
4 inch suspension slam
Aero mods: "Fastback" fairing and rugged air dam and side skirts
Stock MPG: 19
Summer MPG: 27.0
Winter MPG: 24