You really need to find out what is missing when it shuts off. Fuel or spark. Pull a plug wire off and put a small screwdriver into the plug wire boot. Hold it near a good ground about ½ inch in distance. Have someone crank the engine over while you look for a spark jumping from the screwdriver to ground.  It probably needs an ignition module. This would also require a new crank sensor while it's out of the engine. A module from GM is over $200.00, the sensor about $30.00. Don't use aftermarket module! I have had nothing but trouble with them.