I have 2013 Enclave and my transmission started doing the exact same thing about a year after I purchased it (brand new) might I add. And didn't expect it, but ended up getting transmission replaced and luckily it was still under warranty. I kept taking it to the dealer and every time I took it in they told me that nothing was wrong. So I took too anther dealership and they diagnosed it immediately. I hope that's not the case for you, but beware. Good Luck!