The 2.5l can be built to deliver a surprising amount of performance if the rest of the Jeep is built around that engine. You have to keep it lightweight. If you just can't live without the 9000#winch and the 400#s of bullet proof bumpers and tire racks and stuff like that(which there is nothing wrong with), then the 2.5l will probably always be somewhat of a disappointment unless you have some major cash and time to invest in it and then it will still lack the low-end grunt that you need for slow-speed fourwheeling. Gearing can correct this, but an underpowered and overgeared vehicle sucks on the road or when a higher wheelspeed is needed, like when mudding.
If you decide to swap, do not under any circumstances use the AX-5. That transmission is good behind the four because it is light and isn't a big parasitic drag on the engine, but it won't stand up behind any torque. They usually won't stand up to a hopped up 2.5l for very long, so something bigger is out of the question.