If it's a 2008, it should still be under warranty, and the dealer should fix it. Unfortunately, not all repair departments are up on the dashboard electronics. It could be something as simple as the GPS antenna--either the cable isn't connected or the antenna itself doesn't have a clear view of the sky. I'm not sure exactly where the GPS antenna is in the Tahoe, but it should be visible attached somewhere to the body of the car.
My gps isn't working correctly its giving me the gps with the red line through it....What can be done to get the signal again? Or does anyone have any suggestions? Ive taken it to the dealership twice and they can't fix it.