02 Aurora PO420 code

So I had a PO410 code for a while. Eventually replaced the pump and the passenger side value (both bad) and I thought "Well finally the CES light will stay off" So I was out today and of course, it pops back on with a PO420 code. Seems to be a very common code for many cars and looks like the cat is bad. Anyone else have experience with this?

Basically, you look at the plot of the pre and post O2 sensors.....if they mirror each other , the cat is bad.....