FWIW, my installer did not connect the VSS speed wire. I asked him about it, he told me Alpine, Kenwood, etc stopped using that years ago, and Pioneer is the only one that seems to want it.

For the most part, I noticed this when the GPS was off by a couple of feet. Import, when on local streets, and you just missed a turn by a hair..

Yesterday, while GPS had me on the vicinity of the route I was traveling, it was way off. It had me going North, then E, then North, etc - when I was traveling straight on the freeway. At times, even when passing over small bridges, etc, it has me *east* inside the water body and not on the freeway itself.

Has anyone else seen/experienced something similar on your NEX units

Your installer should know better, i would take it back and have him hook it up. There are plenty of posts on here about this. A good installer will hook up everything like the head unit manufacturer dictates, not what he feels needs to be hooked up. 

I have a 7000 in a 96 tahoe and there is no vss wire. My nex learned the truck and my gps is spot on. There is a learning mode for it. Sounds like something is up with it beyond the vss conection.

I had the same problem with it having me going in the wrong direction.  When I installed my unit I didn't hook up the reverse wire.  Once I went in and fixed that, it has worked fine since.  Also, I do NOT have the VSS wire hooked up.