i don't believe that with an intake you're getting anywhere near that much gas mileage. i'm fully bolted on and tuned with the 2.4 mani and tb and i don't see any huge spike in gas mileage at all. to clear things up, you will need to first purchase the 2.4 mani and tb, and THEN put the tune in at the same time to compensate for the throttle body. but tuning a car is pointless unless you're fully bolted because you're gonna want to get the best gains possible with mileage and hp. tuning for a 2.4 tb and manifold and THEN putting on header, downpipe, exhaust after you tuned it is pointless. so get fully bolted before you do the swap and the tune.