re: Diagnose this truck electrical problem

+1 on everyone who has suggested the battery. A bad battery will make modern vehicles appear to be possessed. Last time I purchased one the new battery was bad too.

I had an alternator that decided to suddenly start randomly putting out high voltage and it did a lot of crazy stuff. Finally solved the issue when the battery literally cooked and boiled over.

I still say battery even if it's 6 months old.

Body control module, or PCM, or (i don’t know what Chevy calls this) PDC/smart junction box/ it’s the main fuse box under the hood. Or, could be a ground, could be a voltage problem. Regardless of what the mob says, you took it to the right place to get fixed.

I wouldn't doubt you might have communication codes which can be fun to diagnose. I've seen one module in the line cause failures in other modules. It's just a matter of bypassing the suspect module. I've also seen terminating resistors cause intermittent problems.

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I agree GM makes shite vehicles but engines are pretty durable. My 2914 Sierra engine whose no issues ever other than coil packs going to shite in beginning. But 196k mi

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You brought a vehicle Back From The Future?

Impressive

Do they live underwater, like Hanson said?

Ask your husband.

need a new battery

Open and close driver side rear door.

Change battery if that doesn’t work.

2019 very likely has the original battery.

I'd bet money this is the issue.
After the new battery goes in check output voltage at alternator and at battery terminals