Major improvement in transmission performance. Small power increase, but it's there. I also seen no real MPG gain. Pulls hills better. Definitely worth it. The guy knows his stuff. I have both an 87 octane and 91 octane tune, modest power difference in the high octane tune, so I run that most of the time. To answer 6door , yes you plug the device into the OBDII port, but you have to upload the tune and it over-writes the stock calibration of the computer. So once you install the tune it's always running on that calibration tune until you program it back to stock.