Your GPS signal strengths and DOP values are all perfectly normal.

Are you sure the GPS is calibrated? You do need to go for a reasonable drive of around at least 10min at good constant motorway speeds (60mph) with steady GPS signal for the nav to properly calibrate the wheel sensors to the GPS speed.

When I fitted a Mk4 once I drove for 2 weeks without hitting 60mph and my nav took ages to calibrate - had me on wrong streets sometimes. Once calibrated, it was fine.

Jochen