Ok, so about 3-5 months ago when I first got the Jeep, she had a emissions code problem, no biggy, went through a little bit of a fight to get the right NTK sensors (I installed Bosch ones first) and all was good, the code was gone. Then I had a battle with the TPS sensor. Got that sorted out and now I. Can’t get the P0420 (bank 1cat below efficiency) to go away. The Jeep has 4 NTK 02 sensors (upstream and down stream) that are all 3-5 months old. When I replaced the 02’s I used a endoscope to look at the cats and they seemed fine ( see photo ). My question is do I throw another sensor at it? Or just bite the big one and buy a cat? Something else? Keep in mind this is a persistent code that has been cleared at least 5 times and still comes back. Also she’s a 2001 4.0 5spd with 256,xxx miles if that helps.