‘04 Tundra 4.7 186k miles getting P0420 Catalyst System Efficiency below threshold bank 1 CEL pretty steady now. Initially it was intermittent for months. I haven’t done O2 sensors in years/many miles. Could this be an O2 sensor or bad CAT? What are the implications if it’s a bad cat? I need to tow heavy this coming weekend and am afraid of it running lean. Thanks.