You should probably have this professionally diagnosed before you waste any more money on it. You know all the spark plugs didn't fail at the same time, so while they might be ready to be replaced, that won't cause stalling. The starter has nothing to do with the engine running or stalling.
Loss of just spark is the least common cause of stalling but it sounds like that's what you have. The second would be loss of just fuel. That's almost always caused by a bad fuel pump. By far the most common cause is loss of fuel AND spark due to a common cause. If you're sure you're getting fuel, (you can smell it at the tail pipe), the place to start is by reading the diagnostic fault codes. Many auto parts stores will do that for you for free.
Some GM engines will stall if a signal goes missing from the crankshaft position sensor or the camshaft position sensor. Some will stay running if one of those sensors fails, but once stopped, the engine may not restart. Fault codes related to those sensors don't always set right away so you may need a scanner to view live data and see if a signal is missing.
Most of the time when there's no fault code and you're missing spark OR fuel, it's due to something not monitored by the Engine Computer. That typically means the fuel pump for no fuel, and the ignition module for no spark.
Wednesday, September 10th, 2014 AT 4:30 PM