Alright here's the facts:
- 95 LT1 automatic, no MAF
- Coolant needs to get to 190F or above for problem to occur
- Car parked in driveway and idling
- Engine will suddenly run rough, misfire, backfire and almost stall
- Code 36 shows up, cleared codes while running and it shows up again
- Engine will return to normal smooth operation temporarily and then run rough again
- Its also horrible when throttle is open, undriveable
- Tach is erratic when problem occurs, will blip to 7000RPM at idle

The coil has already been replaced, I'm leaning towards Optispark or Optispark wiring. Could the ignition module also cause problems like this?

Are there any tests I can do to rule one or the other out before I dig into it? It's difficult to diagnose as its intermittent.