[fredjacksonsan]

With the 2.5L turning 31's it's working really hard. Does the Jeep have the stock 4.11 gearset? You might want to look into some 5.88's or something to get the RPMs up on the roadway.

Also, if your O2 sensor has failed it could cause a rich condition; is the inside of your tailpipe black and wet? If so, your mixture is too rich and I'd bet the O2 sensor is the culprit.