Btw, i know this is an old post, but after having my pcm and spark plugs replaced, i was still getting codes...i bugged the dealer and told him that i suspected the cat closest to the manifold. They tested it and said sure enough and replaced it for free under the 8/80 warranty. Everything has been working great since then...i also noticed a significant power increase... Which is awesome!
So it turned out for me the problem was a combination of three things possibly interrelated... Pcm, spark plugs, cat. Theoretically it is possible the pcm killed the spark plugs and the cat.
Hope this help anyone else with these issues.