cutting out the cats will make mileage worse, it has before and after cat 02 sensors. it will throw codes like crazy and run lean like you wouldnt believe. the things i mentioned are the only things that will net you any hp with this engine until the aftermarket decides theres a need for anything else. you have to keep in mind, this engine was designed for use in the dakota, and was placed in the full size for fuel economy, not power. so your kinda working with a limited means already.