1995 GMC Jimmy Running and stalling

The car started to run eratic as though plugs were not firing. The crank sensor was determined to be bad by a diagnostic check. The crank sensor was changed. No change. Then the connector to the crank sensor was changed, no change. Then the tech said it might be the computer. I DECIDED TO TAKE IT BACK HOME. I then changed the coil and Ignition module. No change. Then I changed the plugs, rotor and cap. No change. The car seems to idle at 2000 or lower ok, but never runs smooth when driving. It acts liike it is missing firing some plugs. It bucks and then finally shifts into gear. I checked the spark when it all of a sudfden won't start and it seems like there is now spark. When I get a spark it then starts. Very eratic. It also seems to die after (5) minutes of running. I am at my wits end