Misfire on 5 and 6?

Hello, with an fuel trims reading the opposite per bank, if the Oxygen sensors are operating correctly, I would do a back pressure test on both banks at the front oxygen sensor location. On a V engine that is having trouble breathing (taking in air and letting exhaust out), you can end up with fuel trim numbers like this. Actually there was a case study on a vehicle with these exact numbers and had a restricted exhaust on one side of the engine.
Seeing those numbers, that is the first thing that comes to mind. The engine is very unbalanced right now, with a lack of air flow on one bank, we get a PCM/ECM that starts to try compensating for one bad bank and it effects the other side in the process.
Have you ever done a back pressure test and is the air intake system stock?

This is the video on a fuel trim balance issue from bank to bank. Great video.
https://www.youtube.com/watch?v=hmFozmTf7xg&t=35s

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

Yes , stock intake

Guess I'll be buying myself a back pressure tester kit

Thanks

Go to Harbor Freight, they sell a cheap vacuum gauge that also goes to 10psi positive pressure, which is more than enough to test back pressure. If you have an old oxygen sensor that you can drill out, so you just have the threaded section with a hole in the center.
Next attach a hose onto the adapter and and the other end on the vacuum gauge, and start the engine. Now because youre dealing with hot exhaust, you cannot leave the vacuum gauge on there long, or it will melt. Its a reading you should see on the gauge right away anyway.
You want to see almost zero (0) psi of exhaust back pressure, the max amount is 1-1.5psi, its really nothing. If you have any other questions about the back pressure testing, let me know, and really dont forget to run a quick test due to heat. I know of a mechanic that left the gauge on the exhaust and it melted the gauge and hose.
You could buy a back pressure test kit if you want, its just easier and cheaper with a Harbor Freight vacuum gauge.