Avic D-1 Nav problem

Installed a D-1 into a customers 2005 Ford Excursion a few months ago, except for a few minor issues everything has worked flawlessly until a few weeks ago. The problem arose when we had to swap out the xm satellite radio box and had the d-1 out of the dash. after reinstallation whenever the customer would use the nav. it would route him like normal however when he gets near his final destination it never acts like he is there instead it reroutes him back to the same location sometimes sending him a few blocks away before bringing him to the same location he was just at. When he came back we took the unit back out and found that the pink VSS wire was loose from its quick connect behind the unit after reconnecting everything began working again. well He came back in two days ago saying its doing the same thing we have not been able to replicate this problem at the shop and after removing the unit again the vss wire is exactly where it should be. Anything else that may cause this GPS antenna, software etc. any help would be greatly appreciated. thank you

Also if it helps there is no navtraffic installed on this unit

i would reset the deck, possibly check to make sure the antenna wire is not getting pinched somewhere.There are 10 types of people in the world, ones that understand binary and ones that dont.