1993 GMC Truck GMC Z71 Starts then shuts off after a few se

Has the check engine light come on? Have you noiced the security light staying on or flashing when this happens?

No, no check engine through any of this. Not sure what the security light is....I have no alarm if thats what it is.

If you turn the key to he run position without starting the engine, is there a light that comes on that says security? Also, have you been able to identify if you are loosing spark or fuel pressure when it dies? At this point I question the ignition module or the fuel pump. If the module is bad, you will loose spark. With a bad pump, fuel pressure will drop.

I am assuming that its fuel, just judging from how its acting. Its gotten very difficult to start, once its starts it runs good still until I turn it off again. I can try starter fluid and if it runs on it the spark is good correct? I will do that tomorrow. I ran a power wire straight to the pump from a key controlled source, when I turn the key sometimes I hear the pump run and sometimes I dont, others it will run for a few seconds then stop. With constant power shouldnt I hear it running all the time?

If it runs on starting fluid, it is getting spark. Also, if you ran power to the pump, if will run all of the time. NOTE: Sometimes the pump could loose pressure from a leak which can cause a hard start. If you check fuel pressure, also check how quickly the pressure drops when you turn the key off. It should hold pressure for several minutes.