I have a 2008 Tahoe and has 89k miles on it. We just purchased the vehicle from a dealership in April. Soon after purchase I noticed the voltage meter seemed to fluctuate between around 12 - 15. When driving it does stay mostly at 14. We noticed every once in a while it hesitates a little to start but does start. Now the clock seems to be changing the time to an hour ahead. I went to start the Tahoe once and it clicked a bunch then started. I went and had the battery and alternator tested and they both tested good at Auto Zone. I read past threads suggesting that the battery cables may need to be replaced as other people were having similar issues. The threads did not mention anything of the clock but did mention other crazy stuff going on with lights and door locks, of which I am not having. When I had the battery tested I noticed that the battery was a Mercedes battery. It sounds more like the battery cables to me. Any suggestions?

 

If you have a digital volt meter, actually check the battery voltage with it running, then determine if it is the gauge or the alternator.

 

could be a problem with the battery sometimes a cell can go bad or be on its way out and cause some funky things or could be a voltage regulator going bad inside the alternator.
with a cell going bad in the battery testing sometimes can miss or not even notice a problem because the battery will still show 12 volts. some meters will put a small load on to the battery to test but nothing like what the vehicle will pull while it is running with all of your accessories on.