2008 Jeep Grand Cherokee 4.7L Engine Misfire & P0430 Catalyst Code Troubleshooting

I've been experiencing recurring Check Engine Light issues on my 2008 Jeep Grand Cherokee with the 4.7L V6 engine. The problem started with a persistent P300 code indicating random misfires. I initially replaced the spark plugs and installed an OBD2 scanner with a torque adapter to diagnose the issue. After extensive testing, I found that cylinders 2, 4, 6, and 8 were consistently misfiring. I replaced all four spark plugs and their corresponding coil packs. After disconnecting the battery to clear the codes, the engine seemed to run better temporarily—Torque readings improved—but new live data errors have appeared without descriptions. The most recent fault is P0430: Catalyst System Efficiency Below Threshold (Bank 2). I'm now confused because I didn't know my Jeep had an O2 sensor in Bank 4, Sensor 4. This error appears with no clear explanation in the live data view. Here are the relevant test results from my scanner: - MID:$10 TID:$19 - O2 Bank 4 Sensor 4: Max 40.96A, Min 266.56A, Result: 655.20001A → FAIL - MID:$57 TID:$f7 - Max: 20,480, Min: 55,392, Result: 3 → FAIL - MID:$90 TID:$12 - Max: 4,096, Min: 10,272, Result: 65,520 → FAIL - MID:$90 TID:$27 - Max: 16,483, Min: 26,640, Result: 65,520 → FAIL I'm seeking help to understand what's causing these issues—especially the P0430 code and why O2 Bank 4 Sensor 4 is showing up. Is this a known issue on the 2008 Jeep Grand Cherokee 4.7L? What should I check next? The vehicle remains stock with no modifications, and I used OEM-style spark plugs during repairs. Please advise on how to interpret these live data faults or what diagnostic steps are recommended for P0430 in this model.