I have an 07' Silverado with OnStar. I was told it was XM ready but did not have the correct module in it. I want to instal a GPS navigation in it but would like to stay with a stock set up. I have found a few take out models from other Silverado's as well as other SUV units. Can someone tell me what additional I would need to purchase to instal one of these take out units? I.E. gps antenna, wiring harnes, etc.
The GM part number on the unit I am looking at is #25797978.

Thanks