Thanks for confirming what I thought. Appears that there are two Hall effect sensors in the lock cylinder itself - being the sensors for the Passlock system. I've "recalibrated" the system to the original key, and I even drove the car and did several key-on, key-off cycles.
, the starting problem only occurs after the Security light comes on while driving (by that I mean the light comes on, and then next cycle is a no-start).
Right now it seems like I can either spend $160 for a new ignition cylinder, or I can pay $180 for the Passlock override. The particular system I'm looking at disables all versions of Passlock (assuming it generates the 50 Hz signal straight to the BCM) without actually rigging it with the resistor. This style doesn't bypass it only during startup, as is available for remote starters.
I've seen numerous other "remedies" but all the others seem to be hit or miss. So either I replace the lock cylinder or buy this unit.
How to FULLY Disable Security in GM Cars and remove GM VATS PassKey and Passlock systems
Yeah, I know the page is riddled with grammatical errors. Otherwise, it seems legit.