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I have a 2017 sierra 1500 and it won't crank or turn over SOMETIMES. Originally I went and got my battery/alternator/starter tested at O'Reilly's because sometimes it wasn't starting. Starter tested bad so I replaced it. Ran great for a few days and then wouldn't start. Went back and got it retested and it was also a bad battery, replaced it. Ran again for a couple days and did the same thing. I've replaced additionally the starter 40 fuse, ECM relay, run/crank relay, starter relay that were all under the hood, ignition switch and the anti theft fuse in the driver side panel. For a while I thought maybe it had to do with disconnecting the battery. Every time I'd disconnect it when it wasn't starting, it would start if I let it sit for a couple hours with the negative cable off. I got it in my head that maybe it was resetting a system like the anti theft or something. It still does this thing where it runs great for a few days and then won't start. I'm at a loss and no mechanic around here has a clue. Help!