My jeep has a new engine in it not more than a year old. Yesterday it overheated and it started driving very roughly. My jeep was shaking as it was running. The code on the ODB said that it is the 6th cylinder is misfiring. Replaced it and Jeep is still running roughly really bad. Does anybody got any opinions or ideas? My husband is working on it next thing I told him to do is replace the plugs. If that doesn't work what could it be? My engine has a warranty on it. I just don't know how long of a warranty. It is a rebuilt engine. My Jeep is a 2003 Jeep Liberty 3.7 engine. I appreciate any help I can get thank you very much for your time.