The cost of ring gear and pinion sets to regear front and rear differentials to a higher speed (lower numeric ratio) would be quite high, and gearing up too much will make the truck useless for off road escapades. It would take a long time to recoup those costs in fuel savings.
You could get some advantage by installing considerably taller tires during the week while commuting, and switching to the normal all terrain tires and wheels for your adventures.
One caution: Your speedometer will read slower that your actual speed.
Another alternative is to buy a good used Escort or similar car as a commuter, saving the truck for the weekends.
1999 Ranger Extended Cab, 4x4, 4.0, automatic.