Suburban P0430 trouble codes driving me nuts!

I have a 1999 K1500 Suburban, 5.7 liter with about 115k miles. It has an automatic trans. I am having trouble clearing the P0430 trouble code. I am using a Pro Scan scan tool/meter. The translation of the code is: Catalyist system low efficiency bank 2. I have replaced the cat. converters (about 15 months ago), which worked for a few months. I have replaced both O2 sensors on bank 2. Each time the codes reappear in only a few days (less than 100 miles). I have read some forums on P0430 and tried removing the K&N air filter and cleaned the MAF (sensor). That step bought me the most time, say 200 miles before the code tripped again. Can someone confirm which side Bank 2 is on a 1999 5.7 liter? (I am pretty sure I have it right, but one source listed Cyclender 1 on the opposite side). I would just test the other side, by moving the new O2 sensors, but the O2 sensor is siezed on what I think is bank 1. I will have to remove it with a cutting tourch... which means welding in a new fitting for the new sensor. So needless to say, I don't want to go to that trouble unless it is a last resort. Also, if the Cat. Conv. is already bad... how can I tell if I burned it out with bad O2 sensors? There is no audible rattle while driving the car or when idle in park. Are there other things that can trip this code? Any suggestions or help woulb be greatly appreciated!

One last tidbit of info that may or may not play into this, over the course of the last 15 months when this P0430 code has tripped, on two or three occasions I got a P0302 code (misfire cyclinder 2). After inspection and clearing the code, it does not re-appear. I don't know if it is realated in some way, it seems to come on random.

Thanks!
Ken

bank 2 same side as cylinder #2! A scope following the rear 02's traces would confirm that the conveter was bad! Aftermarket conveters don't have the best reputations!

As with all GM V-8s, cylinder 1 is Driver's side, cylinder 2 is Passenger side.