As Pete said, if it's been running rich for a while it's probably ruined the cat.

Make sure the pre cat probe is switching nicely. Look at the post probe and see if it is fluctuating frequently or steady. Should stay roughly around 0.45v although stamping on the throttle or letting off will cause a sudden change. If it's fluctuating like the pre cat probe then the cat is gone. If it's fine but still high CO then the cat is gone.

Either way I think the cat is gone! lol