Well, you probably need another new cat unfortunately. If it is red hot you probably melted it.
Do you have engine codes with it? Did you check manifolds for cracks when you replaced? Typically you need new manifolds as well, as they are junk and crack pretty easily. This is what throws off your O2 sensors. It's pretty rare that O2 sensors actually go bad so I doubt that is the case. I would check both sides.
If it is still bad, I recommend upgrading to the 02-04 style welded pipe manifold/cat combos. Nissan seemed to know the 99-01 manifolds were junk. Supposedly you also get a 10 HP increase.
Do you have engine codes with it? Did you check manifolds for cracks when you replaced? Typically you need new manifolds as well, as they are junk and crack pretty easily. This is what throws off your O2 sensors. It's pretty rare that O2 sensors actually go bad so I doubt that is the case. I would check both sides.
If it is still bad, I recommend upgrading to the 02-04 style welded pipe manifold/cat combos. Nissan seemed to know the 99-01 manifolds were junk. Supposedly you also get a 10 HP increase.
