2020 LT Z71 with the 5.3, ~3,900 miles purchased new approximately 2 months ago.
I washed the truck Saturday afternoon, let it sit over 24 hours, then went to start it Sunday night and got NOTHING. That's when I noticed I had zero lights or sounds from the truck, and pressing the start/run button resulted in zero change. No lights, sounds, door locks, or power anything. I hooked up a fully charged battery and jumper cables to try and jump it, but the engine wouldn't even crank. The lights and chimes worked, but nothing else. I disconnected everything and now the truck is sitting in my driveway. This is the second time this has happened to me with this truck and I'm not certain whats going on. With a fresh battery connected via jumper cables, I checked to make sure I hadn't left any lights on or anything plugged in to the ports, but no lights were left on and no electronics were plugged in. I have no clue what could cause the battery drain.
However I did notice one thing that might be of interest: I usually press the door lock button twice on the FOB to make sure the truck is locked and the factory alarm is set, but both mornings that I experienced a severe battery drain over night, I found my doors unlocked. I am notorious for forgetting to lock my doors at least once or twice a month, so I wonder if by not locking my doors the PCM, Radio, or some other electronic is not shutting or cycling down? Also, even with a fully charged battery, my doors will not automatically lock if I walk away from it so that again makes me wonder if the electronics are even shutting down when I forget to I lock the truck and set the factory alarm when walking away from it.
Irritating for sure, I'll be calling GM shortly.