Take their advice and check for air in fuel.
I had this same exact problem a couple of times, years ago. Pretty scary passing a car on the interstate, and have your jeep go limp in the passing lane.
Upgrading to the new fuel filter head fixed mine.

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TWO Identical 2005 Liberty Sport CRDS
#1 CRD, 174,000 miles. Eco tune, Samco hoses. Mobil1 0-40w used since day one
#2 CRD 143,000 miles. Bought used (unknown history) with 100,000 miles. Samco hoses.
Eco tune, new rockers, and 5 volt glow plugs installed at 124,000 miles