Update 7/23/2023: Turns out it was a simple connection issue at the fusebox, caused by rust. I must have dismissed this possibility before because I tested both sides of the fuse and it had power, but obviously it wasn't a consistent power source. After discovering this, I cleaned the fuse holder and all has been well and reliable again. I later cleaned the rest of the fuse holders since I started having intermittent brake lights too, and all the electrical works consistently now.

The truck charges good now, however is does not charge at idle which I figure must be related to that new voltage regulator since the alternator will charge at idle when the regulator is bypassed (only for testing - I wouldn't drive it like that).

I have a bad habit of overthinking simple problems, so that is all this was.

Thanks for the help and suggestions.