I have the same problems as you describe. I bought my Sportrak Map in Sep 03. Suddenly the postion is 200 km, more or less, away and high up in the sky. After a while the position is correct again. Satellites is ok all time.
Sometimes it happens every 10 minute, sometimes postion is good for a hour.
First I thought this could happen and was normal. Now I understand that this must be wrong.
It would be intresting to follow this thread and see if anyone else have the same problems.