I wonder if the AIR is kicking in and pumping too much air causing it to lean and detect that as possible damage to the cats. The EVAP setup has a lot of little pieces to it and if one of the sensors or check valves isn't working right it could let too much air in. The EVAP cannister on my old 96 SS the charcoal was disintegrating and there were bits and pieces being sucked up through the lines all the way to the intake. You could pull off the EVAP line and check it. I got a moth full of gas filled charcoal when I did the inhale test!
