92 lumina running rough

Have a 92 lumina with the 3.1 and approx 167k miles on it. Was having problems with car running good for about 20 min and then once warmed up it would die. Replaced coil pack with one out of junk yard. Replaced catalytic converter, wires, plugs, checked for vacuum leaks. After all this it ran fine for about 400miles. Now it is doing the same running rough thing as before but now it always restarts after it dies. getting very flustrated with this car any help would be greatly appreciated.

IAC or EGR?