2001 Z-71, LT, 5.3L - Drove to Lowe's the other day. Truck started at home just fine and ran good to the store. Shopped, came out, put the key in and nothing. No cabin lights, no clicking, nothing. Battery is a year old, but this was worse than a dead battery. Truck was dead. Had a guy jump me. As soon as we hooked the cables, the truck turned over as if nothing was wrong. Drive home, but the idle kept going real low, but if never cutoff.
Today, I hooked up a diag tool and tried to see what might be happening. Truck fired right up. As I was going through some tests, I attempted to kick off the alternator test and boom! Truck shuts off and goes black again. Nothing, no power what so ever. Turning the key and nothing. Just like the other day at Lowe's.
Got the battery charger out with a jump start feature thinking I would repeat the jump at Lowe's. Hooked up, opened the cab door, cabin lights on, beeping because the key is in, turned the ignition, and boom. All black again. No lights, nothing. Dead again.
This is all new to me. Had the truck since brand new. Any help/ideas would be greatly appreciated. Thank you.

 

All I can speculate is a bad ground somewhere? I would start by downloading the electrical diagrams from Charm.li, and then do my best to find and inspect each ground strap. I seem to recall recently that there was one that caused intermittent dead trucks like this that was routed behind the front bumper, on the passenger side. My recollection from the post, likely somewhere on here, is that it was routed through the frame or across the bumper mount in such a way it could fray and short out over time. So maybe it wasn't a ground, but something else, but the symptoms I recall were much like you describe.

Edit: Went and found the post. It is HERE, and worth taking a look at in your case:

https://chevroletforum.com/forum/tah...29/#post512819

Being that the post was about a 2011, and you have a 2001, I doubt the issue is exactly the same, but suspect it might be similar. and I would trace all wiring I could looking for issues like this.

Good luck!

 

For everything to go dead is unusual. I'd start checking between battery and power dist. box. If you're not finding any weak links there, I'd suspect the battery having an intermittent short in one of the cells. When it goes dead again, check the voltage of the battery with a multimeter. If its voltage is low at that time, you've found your culprit. If during this dead mode the battery voltage is good, then tragically, you've got an unusual gremlin. But between the battery and power dist box is where I suspect you'll find your issue, given the breadth of the outage.