1991 Chevy Lumina

I have a problem eith my car shutting off going down the road. But it will start right back up. Then other times the check engine light will come on and run like CRAP. Then the light will go off and run fine until the next time it does it. I have changed the fuel pump and it still does it. I have also changed the well I dont remember what its called but it goes under the packs under where the plug wires goes in to the engine. Not on the side that has the spark plugs.