In my experience this alone will not do it. You may see a mpg increase for a little while or until the jeep learns the changes and adjusts for it. I ended up installing an CAI, 2.5 exhaust Banks Monster and headders. Expensive. I got app 2K in and at least 2 yrs payback on the mpg inc based on my avg mi per year.
If your handy there are do it yourself CAI you could search and not add a lot of cost. I wouldn't do the headers again, but I did like the Banks cat back.
For bigger more noticible gains go for a stroker or V8.