@sam Yupp, @Z15 is correct — the assembly takes place in Flint. Check out the GM Authority manufacturing guide for more:
http://gmauthority.com/blog/gm/gm-manufacturing/
Also as @Z15 said, the Duramax diesels are built in Moraine, as per the GM Authority engine guide:
http://gmauthority.com/blog/gm/gm-engines/
