You answered just one question, the transmission type. If you want suggestions, you're going to have to provide all of the requested information. "Stock". means nothing since even the factory tire sizes varied. Your axle ratio is either 3.07 or 3.73, look at the tag located at the 9 o'clock position located on either or your axle differential covers. Your axle ratio will be embossed into the tag, which ratio do you have? The tag might also say 3.08 or 3.74 depending on which axle you look at.Everything is stock. Automatic. Seem to be getting only around 10 mpg.