2015-2016 GMC Acadia vehicles equipped with a 6T70/75 transmission may exhibit harsh 1-2 shifts, mostly on light throttle, with no DTCs present. In rare cases, the 2-3 shift may be harsh as well. It is possible that the transmission shift adaptive time may not have learned.
Driving procedure to learn 2-3 clutch adapts: Drive in M5 to limit the trans to fifth gear, 38 mph or above about 5 miles on flat level ground at a steady throttle. The use of cruise control to hold a constant speed may be beneficial in the adapt learn drive. After the drive procedure, stop and try some light throttle 102 shifts and drive another 5 miles if needed. Second drive learn may be needed. If so, allow the TEHCM to power down prior to the second attempt. If no change after the drive learn, follow diagnosis for a harsh shift concern.