I too have been having GPS issues with my TB. I came on to this thread last night and found the suggestion about running GPS Status. WOW! All I can say is thank you!
The Navigation program would take forever "searching for GPS" before it would ever lock on. Sometimes it would lock on in a short amount of time, only to lose the GPS signal. Sometimes it would never lock on.
The long and short is that I downloaded GPS Status last night, followed the directions, and tried the Nav on the phone today. From the moment I started it up, and entered my destination, it locked on right away. There wasn't a moments hesitation. It stayed on the entire 63 mile trip and behaved similar for the return trip.
I can now stop looking for a dedicated GPS.