I have a 1999 Dodge Ram 1500 sport with the 5.9L 360. I've been having problems getting the error code "420 - Catalytic Converter Efficiency." I've replaced both oxygen sensors twice with Bosch O2 Sensors and I've also replaced the catalytic converter twice with a Magnaflow High-Flow. After the 2nd Magnaflow went bad I took it to another exhaust shop and they told me that the Magnaflow High-Flow was only OBD I compliant and could only be used on 1996 and lower year models and he replaced it with a Catco brand catalytic converter.
I recently had this 360 put in about 5,000 miles ago my truck was originally a 318 and it went through the stock catalytic converter and one magnaflow on it.
What could be causing this?