Hello & Welcome to JA,
This problem can be a faulty ignition switch ,make sure you are not losing voltage from the switch to the coil & module when this happens.
The problem can also be a faulty ignition coil,module,or distributor pick up coil.All these parts can be tested but if the problem is intermitten it may show good when tested.
Make sure you are not losing fuel pressure when this happens.If it is hard to restart & spraying carb cleaner in the intake will start it for a short period ,you have a fuel pump problem most likely.
I replaced the coil and just put this engine in. The old engine was doing the same thing but i thought that it had to much cam. This engine is stock and has the same problem.
I repaced the engine wire harness and did ohm test on every wire on the harness before I put it in have also replaced the ecm. i have no check engine light until it stalls.when i run the codes i get a 33 and no others.I had this engine balanced and blue printed at houston engine and balance.lots of money invested.I went to have state insection and they said to much unburn fuel in the exhast at slow speed but fine at higher speed. PLEASE help.