08 Tahoe clock adding an hour

[BG1988]

I have this same issue... GPS Coverage area screen on the nav says that the truck is in CST land, but we are really out here in California, which makes the time 2 hours off. Tried disconnecting GPS antenna, re-start, stop, re-connect as suggested elsewhere but no luck. Tried the hidden Nav screen to manually set the time to proper, but within a few minutes it reverts to 2 hours off. Open to other suggestions. For real. Thanks...

go to the secret NAV menu to change it