My R/T is all stock, except for the wheels/tires. I bought a used Diablosport Predator to change the wheel/tire size so my speedometer would read correctly. I also installed a K&N CAI. I saw in the tuner a setting for CAI/91 octane fuel and thought, "What the hell, I'll give it a try!" To my surprise, the MPG (highway) went from 20 to 24! I'm a happy guy! Just hope it passes smog (I'm in Cali).