AVIC-N1 Speed inaccuracy

Anyone out there notice speed inaccuracies with the Pioneer AVIC-N1?  Mine is installed on a 2004 Toyota Sienna and VSS is tapped into the factory wiring (in dash) for the Navigation and the AVIC is showing about 4-5 MPH slower at highway speeds and affecting the accuracy of the indication on the Nav. 

Its connected to the Violet/White VSS cable.  Any Help/comments would be appreciated.

Tried to disconnect the VSS last night and became worse on the Sienna.  So, I reconnected it and tried experimenting to move the GPS unit from inside the dash to under the seat and hoping that the more secured mounting may help???  I finished after midnight and haven't driven the car around enough to get the vehicle statistics to activate yet.  Keeping my fingers crossed...

The new location hasn't fixed it yet.  But I wonder what that 3D and speed and turning learning function is supposed to do???  If it always knows that I'm turning before an intersection and self corrects, wouldn't you think the software programmer could determine a compensation to fix this inaccuracy?  Otherwise, what is all that learning function for?  What version map are you guys on?  I'm on v1.2 - 2nd free replacement.  Well, once the learning is complete, I'll post the speed accuracy result once again.

By the way, when I called Pioneer, they said if I connected the wire properly/securely, it should be dead on.  I called a local installer and he said they connect it directly to the transmission, but to me its all the same wire.  Besides, when I check the connection status, it is getting the signal.....  I guess I'll have to live with the difference.  Will consider different NAV next time...