My gps was working perfectly while i was setting it up with the antena on the dash. When every thing was ok i hid the antenna and now it is a bit slower. You might have the same problem if your antena is not picking up a good signal from the sat.
YOu need to install the antenna properly. Best thing is on top of dash in the middle of near about 2-3 inch to the front window. Just far enough to avoid heat coming out (air), then all should work fine... Be sure igo detectes the good port and baud rate os your antenna.
I had a problem with the antenna location myself, I come to find out that if you have glass that is UV resistant to protect the interior of the car the signal gets partially blocked by this glass. I installed the antenna outside the vehicle and haven't had a problem since.