I just put a Diablo Sport Power Puck on my 2005 CRD, and the difference is amazing. It is adjustable on the fly, and there is a tremendous difference while turning the knob up. The acceleration is far stronger, and even while playing with it, my mileage has risen about 2.5 mpg. With 143,000 miles, I wasn't getting but about 20 on the highway, but after I put on the Puck, I tested it on a 125 mile loop including 90 highway miles, and the rest curvy, 35-45 mph back roads. I then filled it back up, and averaged almost exactly 22.5!
The only downside I can see, is the amount of black smoke from the tailpipe when I get on it hard. My kids love it, but I don't.
Anyway, I would heartily recommend a Power Puck to anyone looking for a sizeable power AND mileage increase.
Just thought ya might want to know...
Rob
Oh yeah...my Liberty is 100% stock.