Hi I have a 2001 3.9 wih the thor engine and I am getting fault codes of cylinders 2 & 6 with a cat damaging misfire I have already replaced all ht leads, plugs, airflow mass meter and coils but still geting the same codes and engine is hesitant when under 2000 rpmand sounds like it is missing a few beats but idles evenly at 750rpm any suggestions