I have an 09 3.6L DI and there are a lot of posts here and on the Encalve, Traverse, and Acadia websites. As some have mentioned, you need an oil with as low of a NOACK rating as you can find. The 3.6L DI beats up both dino and synthetic oils. I am one who feels following the OLM in a Enclave, Traverse, Acadia, or Outlook will result in trouble long before one would expect. You can search the UOAs to see how this engine beats up oil – not so much so in the Cadillac sedans but certainly in the Lambda platforms.
Thus, use a synthetic with as low of a NOACK rating as you can find (some have been mentioned in this thread already), change at 5-6k (assuming synthetic) and ignore the OLM. To best determine how long you can go considering your driving habits and etc. a UOA is recommended. If you plan to have the vehicle no longer than the warranty period then screw it, use what the book recommends and change according to OLM.