I've got a 94' 4.0 with a Manual, getting about 19.5 MPG; driving like I'm running from the cops!!! I use Sea Foam about every 3rd oil change in the tank, but I ran it through the top end of the intake when i first got the Jeep 2 years ago (this is the 3rd Wrangler I've had) & it will make a difference in the performance. It also don't hurt to put some on a rag & wipe out your throttle body, believe it or not you will have some carbon build up in the butterfly & surrounding areas. If you can swap out your air filter for a K&N, it will help with the flow of things through the engine. I love my "Heep", as my 3 yr old says. It's the only vehicle I can count on all the time to get me where i want to go, any time, any place. They would have named it "Marine" but that name was already taken!!! Like Razorus mentioned, a tune up will help too.