1994 GMC C3500 start&stall

You may have a bad temperature sending unit. Because the engine starting problem sounds like a coolant temperature sensor to me. It could be making the engine computer think that the engine is hot when it's really not. A cold engine requires an overly rich fuel mixture because the lack of heat doesn't let the fuel vaporize as well. If the temperature sensor fails and tells the computer it's warm when it isn't, then the computer doesn't provide the right mixture to make the car run well. After the engine is warm, it doesn't matter as much, but it's still not giving the computer the right info.