Subject at hand: 2011 GMC Acadia Denali AWD. 6T75 auto trans. Had my engine oil changed today, and asked the shop to fill/drain the trans oil at the same time. Job done, went to cash out and the paperwork said MERCON V used, instead of GM spec'd DEXRON VI. Knowing next to nothing about AT feeding and care, I stopped dead and asked "isn't that for Ford transmissions?" Service writer said it came from the Cadillac store in their dealer network, and that it was "the same." Doubtful, I pulled up my pdf of the owner manual and it specs out DEXRON VI. No mention of MERCON V at all. Can someone please confirm that one is the same/same enough as the other? Reading a bit I found that the GM 6T and the Ford 6F series trans are a joint venture, so maybe that was the basis of their assertion? Any help would be appreciated.