welcome to the forum
Hope you can find someone local that can appraise your truck? If you learn as you go then make friends,hang out at the local good guy garage and maybe trade some shop clean up for help on the truck.
Go online and read some of the hot rod mags,dont buy them,save the money for the truck. It takes awhile to learn,and help is hard to find and good help is even harder.
It is a little bit difficult to assist you without some details and specs on your engine and drivetrain. However, if you can figure out exactly whats been done to it and whats in and on the engine, there are things that can be done to make your fuel mileage and power improve.