Stumpjmper is correct. Most only get about 1-2mpg better, that's not worth the money. A Dodge Hemi, Ford, or Chevy v-8 will get close to 16 mpg in town and 20 on the highway with the right rear end. 3:08 or 3:55 etc... There is just no real compromise for power and economy.......I use two vehicles. A Dodge Hemi 4wd or Chevy s-10 4.3 marine v-6 when I need a truck then a Geo Tracker when I don't. This has cut my gasoline use in half and has kept the miles off my truck.