Interesting. thanks for the information. Just swapped out coils and plugs which led to a misfire on the passenger side (cracked plug) and now I keep geeting the P0420 code. Thought maybe O2 sensors, but scanner says they are okay. Am afraid the misfire sent enough unburnt fuel to the CAT that it fried. Truck seems to run fine, so I do not think I am having any current fuel delivery or misfire issues.