[LouJC]

The other thing that can cause Cat codes or O2 sensor codes is oxidized terminals on the O2 sensors and the connectors, I had an intermittent O2 code on my old 98 Jeep (high voltage for the downstream sensor) for several years, it would come and go, after cleaning the terminals with contact cleaner it's been gone for a long time.
Changing the sensor could be needed given the mileage on the vehicle, but getting them out, can be a real trial. Need heat and a good wrench/specialty socket and PATIENCE. I had to change the upstream one some years back and had to warm up the engine to get the sensor to budge, and also, you might need a thread chaser to clean up the threads in the bung to be able to thread in the new sensor. Use OEM sensors if you can get them!