Okay, here's my story. I had a catalyst efficiency code if I drove slowly for a while. (more than an hour) one day i got a cel after flooring it up an on ramp. It was bank 1 lean. I cleared the code, and went for a quick drive while watching the live data. When I let off the throttle (to a cruising position) at the end of the on ramp, one of the front 02 sensors would drop to 0.01v and stay there for a long while before coming back to life and reading rich until the fuel trims dropped again. I replaced the front 02 sensors, and now that they react faster the rear 02 sensor doesn't slowly wander up and down anymore, and my catalyst codes and lean codes are gone.