Hi everyone. I have a 2000 Suburban I just bought a couple months ago. I got a couple of check engine codes I've been working through, but I'm stuck on these last three. I have the following current codes: P0175 (System Too Rich Bank 2), P0420 (Catalyst System Efficiency Below Threshold Bank 1), and P0430 (Catalyst System Efficiency Below Threshold Bank 1). I had codes for knock sensors as well, but got them replaced, and only these three codes remain. I took temperatures at the exhaust ports on the manifolds on both sides. Bank 2 was significantly hotter than bank 1. By more than 100F-150F. I took temperatures at the inlet and outlet of both cats. Sometimes the outlet was hotter, sometimes it wasn't. I have a cheap Walmart infrared so I take all temp readings with a grain of salt however. Outlet temps were within 100F of the inlets. I also took readings of the o2 sensor voltages for upstream and downstream for both banks. The upstreams appeared fine but the downstreams were pretty inconsistent. Sometimes staying pretty flat near 0.03v, other times they'd spike. They did this regardless of being at idle, or revving the engine at 2000rpm in park. I'm slightly confused at the information I gathered today, I'm trying to determine what road to go down. I'm good at working on things, not so much diagnosing. I plan on replacing both downstream o2 sensors with new ACDelco's to start, and that should tell me if the cats are bad if the codes come back, if my thinking is correct. But I'm most confused about how one bank of cylinders could be running rich, but the other isn't? Shouldn't all fuel injectors be getting the same amount fuel, at the same pressure? Everything I've found online says if I have P0175, I should also have P0172.