CMoore711
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OP - Have you had any service, maintenance, or TSB work done on your transmission at the dealership since you've owned it?
I ask because I have almost the same vehicle as yours, 2015i Denali XL, mines Quicksilver Metallic, and I'm at 56K miles today. I was experiencing similar symptoms you describe; shudder/vibration at around 30 mph and again at around 55mph, when transmission was cold and initial shift from park to reverse and then to drive was always hesitation and then jolt into gear, klunky downshifts on slowing down. And like you I always felt "this transmission is suspect."
At any rate, I looked up and found the TSB for the hesitation jolt shift from P, R, to D and vibration and took it to my dealer to review while I was going to a standard oil change. The TSB spelled out the whole multiple transmission fluid flush and re-fill and there was even a TCM software update. The dealership assured me that performing those two services would solve my issues, I was skeptical and thought how could a multiple flushes and refill with a new improved trans fluid and TCM flash solve these issues, but they did it and it was all covered under warranty. That service was preformed 10K+ miles ago when I was at 44K miles and it was instantly a different truck, smoother shifts, no more hesitation, those transmission "symptoms" all gone and so far for 10K+miles none of them have returned.
I ask because I have almost the same vehicle as yours, 2015i Denali XL, mines Quicksilver Metallic, and I'm at 56K miles today. I was experiencing similar symptoms you describe; shudder/vibration at around 30 mph and again at around 55mph, when transmission was cold and initial shift from park to reverse and then to drive was always hesitation and then jolt into gear, klunky downshifts on slowing down. And like you I always felt "this transmission is suspect."
At any rate, I looked up and found the TSB for the hesitation jolt shift from P, R, to D and vibration and took it to my dealer to review while I was going to a standard oil change. The TSB spelled out the whole multiple transmission fluid flush and re-fill and there was even a TCM software update. The dealership assured me that performing those two services would solve my issues, I was skeptical and thought how could a multiple flushes and refill with a new improved trans fluid and TCM flash solve these issues, but they did it and it was all covered under warranty. That service was preformed 10K+ miles ago when I was at 44K miles and it was instantly a different truck, smoother shifts, no more hesitation, those transmission "symptoms" all gone and so far for 10K+miles none of them have returned.
