[SQUEEGIO]

Hi guys, I'm trying to help my dad fix his 07 Tahoe 5.3 flex fuel. We have a cylinder 5 misfire and we can not figure it out. I'm using HPTuners to scan and can see the misfire counter climbing steady and feel the misfire at idle. Sets Random misfire & #5 misfire codes along with both banks lean but the lean codes have not come back. Also says service traction control system but that's probably unrelated and more of a coincidence?

I found a little corrosion on the grounds by the thermostat, cleaned that and no change. All fuses are good.
So far we've swapped spark plug, wire, coil, and injector to another cylinder and the misfire stays on #5 no matter what. We took the valve cover off and all rockers are moving like they should. Checked for vacuum leak or exhaust leak but found nothing.

One thing I noticed is that bank 1 02 sensor voltage is very erratic compared to bank 2. There are a lot more spikes in voltage on bank 1 instead of a nice swooping motion like on bank 2. I think the weird O2 readings are due to the misfire though, I can't see a bad O2 sensor causing only one cylinder misfire. I can confirm #5 misfire by unplugging the coil and nothing changes.

Any ideas on what this could be?