Mine '04 was dying after two days of not running it. Some said it was onstar, some said the stereo, but my wrench nephew found something completely different. He found my dash cluster was drawing when the Tahoe was shut off. He swapped the fused wire that stays on when ignition is off, to a fuse terminal that powers off when the ignition is off, and added an inline fuse. Problem solved...for now. My Tahoe is always whining about something electronic, like check this or check that, on and off with messages within the same drive. Whiney *****...but I still love her...
BTW: my clock stays set, as well as station presets, etc