It won't be the fuel, or at least it's highly unlikely to be. You might notice stale fuel by knocking at high revs, but pootling out of the garage in reverse? Very doubtful.
My guess would be an air leak post-MAF, so the car isn't reading the amount of air actually entering the throttle body. Pop the deck and give everything a real good wiggle, see if anything has dried out or come loose.