2002 galant cold start issue

My 6cyl Galant started having issues idling and starting when the weather turned cold. Once it warms up it idles and drives fine. I tried adjusting the idle on the throttle body which helped for a short duration. Ultimately I replaced the throttle body but that had no effect. The check engine light has been on for over a year. The code was for either the rear bank O2 sensor or catilytic converter. Drive fine. Replaced both rear bank sensors. Light doesnt reset after battery was disconnected.
Code now is for a rich condition. Nothing specific.
Any ideas?

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