2004 Jeep Liberty

Engine Performance problem
2004 Jeep Liberty 6 cyl Four Wheel Drive Automatic 95445k miles

i've had an ongoing problem with rough engine performance. Just bought this in sept 08 and dec 08 was told I needed to change the plugs. Did so with no change. Had a compression test done at a garage and was told one cylinder was at 120 while the rest were at about 150. Took it to the jeep dealer (still under warranty) and they did another compression test and found all cylinders about 170 with the one in question about 179. Took it to another jeep dealer. They were going to perform a cam and crank test but instead said I needed to replace the plugs (to a "Jeep" approved brand) and did a major de-carb. They said I had a slight misfire in one cylinder (10 out of 200) I still have the same problem.
it kinda "hiccups" when idling and is worse when hot any suggestion as to what I need to have tested to find out what is causing this? I've already spent a small fortune and still have gotten any answers.
thanks