I had my XLR into the dealership today for a minor issue and mentioned to them that I noticed the GPS system was constantly unlocking from the satellites. I have two other cars with GPS and once the system locks on to the 3-4 satellites it usually never loses the satellites unless you're in a tunnel.
To my surprise when I returned to pick up the car they said that they were able to fix this issue as there is a GM bulletin on it. Unfortunately I was in a rush and could not pursue the questioning to find out more about what the bulletin was about. Maybe Allen can find out for us. On the way home from the dealership, the system did not unlock from the satellites at all. So maybe it is really fixed?