I live in the northern Rockies. but, the navigation problem is one that shows the signal as red--no signal--after anywhere from 1 to 5 hours into the day. often, it will start up after we get gas or have lunch, then quit again after the next stop. so it is not an issue with location--gps works nearly everywhere we would want to be--and it is not an issue with the antenna, as that was replaced. I think there is something in the unit that is sensitive to heat buildup from the radio and that causes the problem. the challenge is that when we take the unit in for service, it is just a few miles away, so the system is working. and of course, the service people say there is nothing wrong, except for dirty discs, which of course are not dirty because they are brand new.