I just installed a GTE Performance Chip that adjusts the fuel/air mixture and the timing. Took me 10 minutes; cost me $79 from http://www.performancechiptuning.com
They say it will take at least a week for the chip to "reprogram" the ECU, but after 2 days, I am already seeing a 1.5 mpg increase. We'll see if it's "snake oil" or not; but if it makes my engine run more efficiently with more MPGs and HP then it was worth it. Can be removed just as easily too if necessary.