For what it is worth, I would not go this route unless some one gave me a free fully functional nav unit. I have the Nav in my '07 Tahoe and have been less than impressed. The brightness adjustment sucks. It is usually bright as crap at night and dim in the daytime. The nav requires dvd purchase to update the system. It still wont work in many neighborhoods, some of which are older neighborhoods from the 80's. That being said, it has been useful through a cross country move, several cross country trips to visit family, and just general exploring of a new city/area.
If I were going to go through the hassle, I would find a way to use a tablet as a head unit or just find an aftermarket unit that I like. I have even considered setting my phone up as a HUD.
I forgot to mention that the backup camera is pretty freaking awesome, especially if you tow frequently. However, most aftermarket head/nav units support backup camera.
