I did run the KOER test and came up with nothing.
Meaning "nothing" nothing or "111 pass" nothing? If it's the latter, it suggests that the problem might be intermittent, which could make it more difficult to diagnose.
I have pulled the plug and # 5 is dead and fouled out big time as in not firing at all.
Fouling of the #5 plug strongly suggests to me an intake gasket problem. A lot of the times it seems that an intake gasket leak seems to hit #5 worst. A leaking intake gasket can allow excess air in (this is often associated with ping/spark knock), and/or allow oil in, and/or allow coolant into the cylinder. Coolant will poison O2 sensors. So any one of these things (vacuum leak at intake gasket, poisoned O2 sensors, or misfiring cylinder due to fouled plug) could, individually or in combination, trigger the O2 sensor code. So, at this point, I would suggest you figure out why #5 is getting fouled, and see if that resolves the issues.
Often, these intake gasket issues are simply due to bolts that come loose, and they can sometimes be resolved by simply going through and tightening the bolts down. Other times, the gasket needs to be replaced.
And, of course, there are other possibilities beyond intake gasket, for these issues.