Have you driven it yet? Any odd noises from the rear diff?
Have all the recalls been done (vent tube on diff, etc)?
I picked up my 2006 NA with 66,000km 3 years ago and it has all the same options as yours. I found the rear diff groaned horribly. I ended up swapping out the diff fluid for Royal Purple 2 years ago and all is good. Total cost was $60 CDN for the fluid (I did it myself).
GM really struggled with the diff fluid on these LSD cars. With only 5100 kms, I highly suspect it doesn't have the correct fluid in it.