I recently purchased a 2011 Enclave and while reading the manual attempting to figure out all the new electronic stuff, I discovered that it "required" a new oil.
dexos is what GM call it and a little research on the internet indicates its formulation is different enough that the API will be using the designation "SN" for this oil. ILSAC grades it "G5"
In both cases this is one designation higher than the present standard for the best (non-synthetic) oil.
Information on the internet suggest this oil will not be readily available at retail outlets until spring. In the mean time GM seems to have the upper hand with statements like this in the owners manual.........
"Failure to use the recommended engine oil or equivalent can result in engine damage not covered by the vehicle warranty"
I don't know it it was intentionally done in conjunction with the oil change but they also changed the oil filter. Earlier 3.6 V6 engines used various versions of the PF61 filter with a 13/16 thread. The 2011 engine in my car uses a PF63 (which I cannot find) which has 22mm threads.