Im not sure whats wrong with my 95 z28. When im driving everything would be fine then the car would stumble a little and the SES light would come on then the car would continue to drive then just turn off a couple minutes later and the check gauge light would come on. i would have to let the car cool off a few seconds before it will start up because if i try to start it after it shuts off all i would get is cranking sounds. I have swapped my ICM with another one but my car still turns off. Im thinking to check the ignition coil next then maybe the opti spark? any suggestions?

 

Doubt it's the coil but they are considered "tune up" items and should be replaced periodically.

I think you should try heating up the opti with a blow dryer and test it. A scanner wouldn't be a bad idea either.

 

See what the codes are. I have had the ignition switch go bad and also a fuel pump and could drive for months until it just died for good. Would get worse each time it happened and more often. Very similar to what you are describing. The fuel pump would do it most ofter above 85 degress. The ignition switch whenever.