I seem to have inherited the dreaded random stall issue. I've looked all over the net and several different forums and it's obviously a very prevalent problem as these cars age. I can't say that I see a definitive single problem that is a permanent fix. I'm sharing my story in the hope of helping others to find a remedy.
So , here are the facts....
It's a 94 Z28 M6. It's a bolt on car. I've owned it since '06. Mileage is 158K. Pretty much trouble free until lately. I hadn't driven it much for the last 2 years. I did run it every few weeks in an attempt to avoid problems such as I am having now. The vehicle has been in covered parking and a cover placed over it. I did use a fuel stabilizer in the tank to try and keep fuel usable. I've been wanting to get the car back on the road and I have been refreshing everything since March. I ran the old fuel out and it now has fresh gasoline.
Fuel pressure is within tolerance. I have a pillar mounted fuel pressure gauge and I did notice that when a stalling event does happen that fuel pressure holds according to the gauge. I have verified that the Fuel pressure gauge is accurate by testing pressure at the fuel rail.
It has stalled cold and warm , idling and driving, the stalling while driving is pretty unnerving to say the least.
The VATS resister bypass was done back in 2011 and never had an issue between then and now. Around the same time I did have the distributor give up , it was the original one. That one gave me plenty of warning when it failed with heavy misfires and DTC's . I replaced it with Autozone purchased unit. I don't remember the brand but I remember that the cap and distributor were sold separate and it was around $380 at the time. The distributor doesn't have many miles on it , 2 or 3K maybe. Ran like a champ up until now. I'm not getting any misfires at all. It literally just shuts off.
When there is a stalling event it will eventually restart but it seems to take a few key cycles to get it started again. I do get a security light while the car is moving. Stalling seems to follow a few minutes after the light comes on. Not always the case though.
On cold start all the gauges and lights perform their checks normally. I have noticed an odd event with the security light though. With the car idling I can get the security light to come on for about 5 seconds by turning on the headlight switch. I've had it stall a few minutes after the light came on and went out.
I have an Actron C9185 scanner and the only codes stored were DTC 077 and DTC 048. These were of my own doing when I inadvertently left the MAF sensor unplugged and started it. I have since cleared those and no other DTC's are currently present.
I have thrown a couple of easy fixes at it hoping for an easy fix. I have replaced the ICM and Coil. New battery cables , both positive and negative sides. cleaned all battery connections and grounds. I've done a wiggle test on underhood wiring harnesses and connections while the engine is running with no stalling events. I'm leaning a little to an issue with the fuel enable circuit , However I'm doubting the TDR or BCM. The way I understand it there is a fault enable mode that will not shut fuel off if the car is in motion. I have a VATS bypass module that I have not yet installed. I was hoping to find the issue somewhere else before cutting in to the wiring.
Thanks for any assistance everyone.

 

If you were losing the 50Hz fuel enable signal from the theft deterrent module (there is no BCM in a 94) the PCM would set DTC 46. And as you noted, if any part of the PASS-Key (VATS) system fails while the engine is running, it will not cause the engine to shut down, and it will allow the engine to be restarted when it is shut down using the ignition switch.. Additionally, when that happens, the SECURITY light comes on and stays on to alert you there is a fault in the system.

From Shoebox, which it appears you have already read:

4th Gen LT1 F-Body Tech-PassKey/VATS

Before replacing the ICM, did you have the old one tested? It's possible the new one is defective as well, and has a problem with heat soak. Have you spaced the ICM bracket off the head to reduce heat soak?

4th Gen LT1 F-body Tech Articles

The fact the SECURITY light sometimes comes on when you turn on the headlight switch may be pointing to a problem with the ignition switch. Does this happen when the headlight switch is turned to parking lights, headlights, or both? I'd have to look at the wiring diagrams to see how this could happen. Nothing I've ever heard before. But after 25+ years, ignition switch problems are becoming more frequent.