Performance? I doubt it. The basic word on the 4.0L is that you're not going to get much more power out of it unless you're increasing displacement. The header might give you a little, but the converter is fine in stock trim.
The sound might change a little. I think you'll do more with a muffler change, though.
If it's worth doing, then it's worth [I]over[/I]doing.
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The build, the gear, and the mileage: [URL="http://www.jeepforum.com/forum/f22/wasteland-survival-guide-engineering-greta-1344782/"][B]The Wasteland Survival Guide[/B][/URL]