Carl's 68,
Looks like you have the primary stuff checked. If it cranks it's not the starter. I would suspect the throttle position sensor and the fuel pump. If it's the fuel pump then it's bad or just a faulty ground. Guess where the fuel pump is? Yep, if its like the trucks it's in the fuel tank. Next time it happens have some one crank it and check to see if its getting fuel. If it is then its problem probably lies in the ignition system.
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Gerardo
1983 Custom Truck
TX Plates: "BAD BOW"
http://www.geocities.com/abetterchemist/