Same problem here with my shinning new S3!!!

I'm on navigation 6.9. Your description is perfect: The screen starts jumping, jerking, freezing again, then glitching to hell...

Then I get a black screen, where the maps should be... But the voice and my position is still accurate....

GOOGLE, SAMSUNG, GOD, anyone!!!

Solution please!!!

In the mantime, Patrick, how do it install the version 6.1?

Thanks mate..

Diego