I got a little better miliage out of my 98F-150. Mine was gutless as hell for towing so I bought one and ran the towing package and changes a few shift points. it made a big difference. easier on the engine which usually means better miliage.
Before I would barely get 180miles out of a tank of gas going through the mtns towing the machines (slightly heavy on the right foot at times), now I can go about 250.
between the supertuner and extra leafs in the rear suspension, its actually nice for a 1/2 ton, but my 5.4l still sucks gas.