Check fuel pressure in the engine bay with fuel pressure gauge. Should run at 55 psi at start-up, dropping to 3-10 psi at idle. If low fuel pressure, you need a new fuel pressure regulator.
It could also be that you need a new inline fuel filter; cheap easy fix.
It could also be deposit build-up in the EGR. How would you know? If car is warmed up and in the 'D' drive position while idling and it stalls.
Another quick check would be to purchase a GM OBD1 decoder ($40) and find out what engine flash code is turning on.
I suggest you do a quick and cheap maintenance check first before major repairs.