It would help us in helping you if you gave us some more information, like what do you use the truck for? how much mechanical knowledge do you have?
My parents have a Ford Ranger as well, and we found that the best way to get better mileage out of it is to not use it, my dad bought a $250 Honda civic that gets 40-45mpg compared to the 18mpg the truck gets and if he only drives 2,000 miles (just over 5 miles per day) a year he will still save $200 a year in gas alone, that is close to the number of miles that you would drive if you just made a 40 mile round trip to buy food once a week.
If you rent insted owning where you now live, I would think about moving! if you figure out your cost per mile to drive (all vehicle costs added together, divided by miles driven per year) and add that to your cost of rent, or how ever you figure out your cost to live in a new location.