I'd mention a couple of things:
1. Spend a few bucks and get a battery disconnect widget that lets you disconnect the battery just by unscrewing a knob. I'm constantly disconnecting the battery, especially when dealing with anything electrical or fuel-related.
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2. I had a devil of a time with my 1993 80 seemingly stalling out when going uphill. It turned out to be a faulty connection to the throttle body. These are pretty old trucks at this point and often have been fiddled with and the connectors come loose or were not properly repaired. Have a close look and tug a little on anything related to the EFI. Might reveal something.
Are you getting a Check Engine Light when the truck stalls?
Hope you find the culprit soon!