Gordenf
I'm scratching my head on this one. The only thing I can advise you to check is the ground buses for corrosion https://www.gmforum.com/t278980/ and then clean and inspect the battery cables and terminals https://www.gmforum.com/t278927/.
If after you do that you still have a problem, come on back and let'* see if we can find something else for you to look at.
If after you do that you still have a problem, come on back and let'* see if we can find something else for you to look at.






