Adding a navigation system to a 07-08 Trailblazer

[Ray62406]

Hi, I have a 02 Trailblazer with 138k miles that got hit from a hit and run driver. Since it has been so good to me I decided to buy another late model while there still are low mileage units out there. I had the chance to drive a GMC Envoy with a navigation system and would have purchased it had it been 4wd.
I haven't seen a Trailblazer with a navigation system but found a number of units on car-part.com and other places. Has anyone tried to upgrade the existing entertainment system to a navigation system? I'm sure they will interchange and plug in but I am concerned about having to have a dealer program the pcm if necessary. I would venture a guess the service manager will get glassy eyed if I brought one in for something like that. (you don't know our local dealer like I do).
Will it basically be a plug and play swap or am I better off finding a Trailblazer with the navigation system already installed? They seem to be rare....