Hi,
The P0420 indicates the catalytic converter is operating under the threshold. In most cases, it is the converter and not the O2 sensor.
As far as the slipping, the best thing to do is a line pressure test to confirm there isn't a low-pressure issue resulting in the slipping. There is a pressure control solenoid mounted in the valve body that may be failing.
I attached pics of the sensor I'm referring to.
Let me know.
Joe
See pic below.
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Thursday, July 28th, 2022 AT 12:54 PM