USMC-0341

Same thing happened to me with my 2018 Denali 6.2 liter 4x4. It would start vibrating at 62 mph. I had just purchased it with 58,000 miles on it. Since the salesman didn't have me drive it on the highway (to much construction going on), I ASSUMED it ran fine at higher speeds. Biggest mistake i ever made. My bad. GM dealer said it was tranny. They flushed it with (supposedly) 20 quarts of Mobile 1 transmission fluid. That helped the vibration some, but I hate the way it shifts. Roughest shifting truck I ever owned. Though slight, It's just noticeable to me everytime I drive it. Mostly through the first 3 or 4 gears, then it smooths out. Ask your dealer about a bulletin concerning your year and model, and if a transmission flush would help your vibration problem. Good luck! Joe