I'm in the same boat, more or less.
1988 Fiero, 1999 Buick Regal PCM and engine.
Flashing a calibration after cycling the VATS setting from serial to PWM and vice-versa (and turning off the code reporting) has no effect.
Car starts and immediately dies.
All of the sensor inputs are reporting and the car runs gloriously for that 1/2 second.
Back-probed the injectors and they are not firing after that initial fire-up.
So far, those 2 credits i spent on this PCM haven't paid off...