After reading this string of replies last night I decided to drive to my local muffler shop and replace my HUGE RESTRICTIVE factory muffler with a 2" straight pipe. I figured that this was the cheapest ($65) and easiest mod to perform, actually this was my first modification.
The extra noise is not at all what I expected, just a nice rumble, not too loud. The sound is quite nice.
When I left the muffler shop, the diesel seemed to stutter a bit. So I stopped at a NAPA Auto and installed a new air filter and ran it hard through a few stoplights. This seemed to fix it. I thought that maybe the computer needed to adjust to the new setup(??)To me the the Jeep runs better. Time will tell...

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2006 Liberty Sport 4x4 CRD, Cat-back straight pipe, ORM, 255/70/16 Michelin LTX M/S, no lift, Fumoto