To me it definitely sounds like a voltage problem. GM's are bad about voltage regulators that quit working correctly when warmed up. And their regulators are built in to the alternator, meaning you have to either rebuild or replace the alternator. Given its age, I would replace it rather than rebuild. Definitely have the alternator and battery tested and see what is what. AutoZone, Advance Auto, and O'Reilly all test batteries and alternators for free and it only takes about five minutes.
And as suggested above, make sure that the terminals are super clean and tight enough that you simply cannot move the terminals by hand.
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Friday, March 16th, 2018 AT 4:03 AM