'05 Tuscon V6 coded a misfire in cylinder 5. It previously coded an issue with the o2 sensor in bank 1, sensor 2. I didn't have access to a live scan tool and that sensor is a pita to check with a volt meter so I checked the spark plugs first. The plugs in 1, 3, and 5 had some carbon deposits like it had been running rich, but they were also extremely worn like they had been in since day 1 and for 130k miles. The plugs in 2, 4, and 6 seemed to be running a bit lean (white deposits) but not too serious. Bank 2 o2 sensors have not reported any issues. I replaced all the plugs and checked the wires' resistance. They were perfectly in spec with rubbery, supple insulation so I left them. The worn plugs were enough to cause the misfire, but it still doesn't quite explain that the downstream o2 sensor had previously had issues. I borrowed a live scan tool to check the sensors and the downstream sensors in both banks 1 and 2 aren't quite as steady as I think they should be. They seem to mirror the high/low voltage fluctuations of sensor 1 in their respective banks but the fluctuations are only about half as frequent. Is this normal or is it pointing to failing cats?