I had this issue and found the answer from a friend of mine that ran several GM Dealer Service Depts in our region for many years.
Not saying you shouldn’t check for a parasitic draw. I did as well and found no indication of a parasitic draw.
What my friend told me is that there was a GM Service bulletin for my 2007 Tahoe (and other year and similar models) that you needed to change the Negative Battery cable. The bulletin indicates that the cables develop higher resistance over time and that keeps the battery from fully recharging. I thought this sounded odd, but if you really think about it, it makes absolute sense. Everyone (including me) thinks that if the alternator is producing enough Volts, that you’re golden. But nothing could be further from the truth.
The thing that keeps your battery charged isn’t Volts alone, but the Current, or Amps, that are able to flow to the battery. Too many Ohms, or Resistance, less Amps, or Current flows to the battery. Volts divided by ohms equals Amps.
Long story short, I replaced the Negative battery cable and problem solved. If you can’t find a parasitic draw and have tried other things, you might change the negative battery cable. But be ready if you do it yourself! Not fun….goid Luck!