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I am having the same problem. Purchased first Denali XL in June and it was in the shop for various reasons for over 60 days. Needed a new steering column because it was binding and 2 inches shorter than correct part. Took a long time to get one. They bought me out of it and I bought another one that is an 8 speed. Didn't know they were changing. Took delivery end of November 2014. Had a problem with the AFM immediately and the GM dealer "couldn't hear it". Hooked it up to a computer and said it passed with flying colors. Said come pick it up. Called GM customer service. Worst ever customer service experience. Runaround. Demanded I get access to my local cadillac dealer for service. Took it there, they noticed the flaw. Said the AFM system wouldn't come out of V4 mode soon enough and caused the engine to labor and caused serious valve noise. and GM customer service said there was nothing wrong with the SUV. More than once. Week before last, check engine light comes on, traction control light comes on and collision avoidance system "unavailable". Called cadillac dealer, they towed it in on a trailer. Next day they said a service bulletin was out on it. It was issued in late January. For several years worth of GM SUV's. Fix is to replace left side valves (running cylinders in V4 mode) and oil pan and oil pump. 10 hour job. 1750 on the odometer. I'm not confident this will fix the problem because the computer for downshifting seems to be the problem. Would think software adjustment, but GM customer service says vehicle is operating as designed. Told me I was too picky. I have owned an 07 yukon, 10 Denali, still have a 12 Denali and 14 Denali XL. Never any problems. This 15 is not ready for prime time.