Automatic Transmission Torque Converter problems of the 2011 GMC Acadia

The car shutters intermediately when driven at higher posted speed limits. From about 40/45 miles per hour up to about 60 miles an hour. The vibration shakes the entire vehicle. Letting off the gas or acceleration will stop it, but go back to a steady speed, and it returns. Have kept up with service and the vehicle is in tremendous condition, but this condition is present in all weather and temperatures and seems to not have a cure. Have replaced all possible causes, including torque converter and possible sensors. Has not gone away. Noted that other owners have posted similar/same complaints on the same year and make. Same complaint with sister car 2011 Saturn outlook. There is a problem with the drive train and needs to be fixed. Understand some people have found a damaged "d plate" in the transmission-but replacing the part has resulted in the part failing again and the problem returns.