So why are you looking for more power? Looks like you've had the Jeep for a couple days dude, don't underestimate the 4.0L I6.

Not without help.

Couldn't be more incorrect. The XJ's unitized frame is a distinct sub-structure critical for the strength of the vehicle:



Otherwise there wouldn't be anything for "frame stiffeners" to go on to, now, would there?

Monocoque unibodies like a Honda Civic don't have frames.

 

http://en.wikipedia.org/wiki/Jeep_Cherokee_%28XJ%29

I'll just leave this here. OP you need to READ UP on your vehicle, to understand what it is you have. Then you need to start reading the threads on this site. This is the only way you are going to learn. If you want to know something specific, do a search. I can almost guarantee it has been covered many times before. There is a lot of info out there, and you should have no issues finding thing to learn. But you need to start doing it first, LOL