The code was thrown again after I replaced the cat, both o2 sensors, plugs and wires. I have checked the SAIP and EGR valves. They all work.
I compared the o2 test readings between bank 1 and bank 2 for all four sensors. They are virtually identical. Difference of .1 volt.
When I changed the plugs, the plugs on bank2 where uniformly lighter than the plugs on bank one, which were uniformly browner.