Divide and conquer.. the 3 areas ...Spark, Fuel source, Fuel inject.
**The vehicle powertrain electronics need a good stable power source such as an alternator and solid battery connections, information connections and grounds.
* As far as troubleshooting you need assistance. Somebody or a test aid.
What I mean is trobleshooting needs either someone to crank while you quickly test for spark or some test setup to inform you while your cranking the disfunctional engine whats not working.
* Find a situation that can repeat the problem safely.. such as running the car in the driveway being sure it doesnt overheat. Driving on low traffic road with an accompaning vehicle or cell phone.
I believe its not the Security VATS system because it is designed to allow for safe driving by not disabling while driving.. It turns off fuel pulses.
It could be your IM (Ignition Module)... or associated wiring all the way back to the PCM. Symptom :
rastic cut of power.
Find a junker IM or even a PCM and swap the chip.. (easy swap)
* Fuel Pump.. When it stalls go and press the Shrader valve on the fuel rail and expect a good spray or if it dribbles you lost fuel pressure.. (35psi).
but often irractic power and no start and more various symptoms like chugging before it stopps.
* Fuel Pulses.. Controlled by the PCM. (I think) disconnect the Camshaft sensor and see if the car runs or doesnt stall. (GM advice) (easy swap.. $20) It could be failing while the PCM is using it.
Some Ideas.. here.. hope it helps.