For the last week i've been running 100 octane gas on the 100 octane APR program....and tonight i switched back to 91 in anticipation of filling up with 91 sometime tomorrow. Once again, night and day difference. not as drastic as stock to chipped, but the 100 program pulls noticably harder AND gets better gas mileage to boot! I haven't filled 91 yet...and i'm not sure i can bring myself to do it or not. power or cheap(relatively) gas? what should I do? hmm...