I had this issue too. I was using Google Maps and it would show me off the road, like I was a thousand feet left or right of the actual location. I tried moving the phone and disconnecting and re-connecting. The Google Maps app worked just fine in the phone on its own, but wasn't happy when I connected to the car via USB. Only way I could get it to correct itself was to do a soft reset of the head unit (use the power and skip buttons together for a few seconds) or reboot the phone. Maps hasn't gone crazy in a long time. Only thing that's happened since are either phone/app updates or making sure Sync was on the latest version.