Before going to the track yesterday, we replaced the plugs in my 396 Stroker. Several had pretty heavy carbon deposits in them, but those that didn't had slightly wider gaps ~0.045". I set the new plugs all for 0.045". I don't know if that is related, but since reconnecting the battery, I'm getting 6 DTC codes. Prior to the plugs being changed I had seen an occasional 33 and 43, now I'm getting 16, 18, 36, 41, 42 and 43 as well as the service engine light.
Any ideas on where to start the troubleshooting?
And even with the codes, it managed to run an 11.8 with a wheels up launch on a hot track.

 

Sounds opti related. I would start by checking your opti harness for corrosion. Must be intermittent to be running that good.

 

Unplugged the battery, checked over the wiring but didn't find anything and reconnected the battery. Now, I'm getting 36, 41,42, 43 and 51. WTF?!
The codes are still there as is the SES light. Unfortunately, the GM Service Manual that I have doesn't have section 6E, the Engine Electrical section. That's in bood #2.

 

There is a list of codes on my Tech Page. Still sounds opti-ish. Do you have a knock sensor? That's what 43 is for. How many max rpms are you hitting?

 

Yes, I have a knock sensor and 6500rpms.