Seems like it could be electrical. Possible coil wire loose, loose DME connection etc. Loose ground wire.

New update. Replaced the fuel rail, and took the car out for a run in the back roads, and that shed a lot of light on things. Most importantly, the condition does not only happen in corners, but variably at part throttle. On a racetrack, coming out of corners is just the only time you're in that situation. If you make it to wide open throttle smoothly, you're good, but if it stumbles on the way there, then it takes some time to clear out before it pulls cleanly, wide open or not. So I think that theres a problem when it's try to meteter fuel - running way too rich at times, which then wets the plugs and causes the misfires, until dries/clears out.

The coolant temp sensor it reading the correct # of Ohms, so it looks good. I'm thinking either the flapper door, or the 02 sensor is the problem. It also seems the problem only occurs once the car gets pretty hot.

worn wiper tracks on the AFM maybe?

I had that on one of my AFM units, but the problem looked different on track. Still pop the cover of the AFM and look for deep grooves where the wipers run. The fix is to bend the wipers to run on new grooves.

Will do, thanks Joe. My donor is clean, but has nearly 1/4 million miles, so this is quite possible.

The wiper tracks did look worn, but bending them to get the wipers on a fresh surface didn't help today. A few more observations. This only happens when you been off of the gas for a while, and then go back to part throttle. If you then get out of it when it's stumbling, and jump right back on full throttle, it pulls cleanly. If you go back to part throttle it again stumbles for 4-5 seconds until clearing out, and pulling cleanly from then on, part throttle or not.

Can you swap AFM and DME from another car.

This is sounding stranger as it goes along. Athough remember full throttle is open loop mode. IE running the map in the chip. part throttle goes closed loop and it reads the O2 sensor. As such the car works different under part throttle vs WOT.