1980s 5.7 L TBI engine. Stalls while stopped and idling.

I really want to avoid wholesale parts swapping out if I can avoid it.
The problem doesn't seem to occur until the engine is well warmed up. The idle speed generally seems to be at its normal level at this time. (no tach installed)

When stopped with vehicle in gear. (IE traffic light) The idle will suddenly and randomly drop causing the engine to stall. This happens anywhere from 3 - 45 seconds after stopping. It does re-start pretty easily.
But:
When stopped with the vehicle in Neutral or Park. It does not happen. (Or hasn't started happening yet at this point) But it will occasionally stall 1-3 seconds after shifting the vehicle into gear.

If you maintain a slightly higher idle by slightly depressing the accelerator it will not do it in either case.