I have the same problem with the GPS.
I checked it with other phones and found with the others is there no problem. With navigation software like Here, TomTom, Navigon and so on, often the position is on the wrong road. In cities it is not funny to find the right turns.
At the end of a tunnel you have to wait some seconds more as with the others test phones to catch the position back.
I tested this in different kind of cars.
Out side the car and with low speed, like bicycle rights, it looks like better and the tracking look like ok.
There is no difference when the settings for GPS will be changed.
Also calibrate the sensors doesn’t help.
Then I could see with the app GPS test or the app Locus the phone has a very high accuracy of 3m more or less but the signal is jumping around the position and was not on the right position. At the test time I was still on the same position without movement.
With my other phones (Samsung, BQ, Sony) for test the accuracy which was displayed was not so good but the position was right and stable on the same place without jumping around.
Hopefully there will come a software fix for GPS otherwise it makes for me no sense to use an outdoor phone with bad GPS handling.