1999 Chevrolet Suburban P0430 Code: How to Fix Catalytic Converter Efficiency Issue on Bank 2

I own a 1999 Chevrolet K1500 Suburban with a 5.7L V8 engine and approximately 115,000 miles. The vehicle has an automatic transmission. I'm currently struggling to clear the P0430 diagnostic trouble code, which stands for 'Catalyst System Low Efficiency - Bank 2'. I replaced both catalytic converters about 15 months ago, and they worked well for a few months before failing again. I've also replaced both oxygen (O2) sensors on Bank 2. However, the P0430 code returns within just a few days—typically less than 100 miles after replacement. I’ve tried various troubleshooting steps: removing my K&N air filter and cleaning the MAF sensor. While this extended the time before the code appeared (about 200 miles), it did not resolve the issue permanently. I'm trying to confirm which side Bank 2 is located on a 1999 5.7L Suburban. I believe I have it correct, but some sources indicate that Cylinder 1 is on the opposite side (passenger side). If Bank 2 is on the passenger side, would testing the other bank by swapping O2 sensors help? Currently, the O2 sensor on what I believe is Bank 1 is seized and will require removal using a cutting torch—this would involve welding a new sensor fitting. This seems like a last-resort option. Additionally, if the catalytic converter is already failing, how can I determine whether faulty O2 sensors contributed to this? The vehicle runs smoothly with no audible rattle during driving or idle in park. Are there other potential causes of the P0430 code? Any advice or insights would be greatly appreciated! One additional observation: over the past 15 months, on two or three occasions I've seen a P0302 code (Cylinder 2 misfire) appear. After inspection and clearing the code, it does not return. I'm unsure if this is related to the P0430 issue—it seems random. Thanks for any help! Ken