This is a duplicate report. Not sure prior report was transmitted. Average traffic and a clear day with a dry road (Interstate highway), while driving at the posted speed limit of 70mph with cruise-control engaged, the 6-speed automatic transmission suddenly downshifted to a lower gear (See NHTSA Campaign ID: 19V075000). The downshift caused the vehicle to slow with a rough and sudden jerk which could have resulted in loss of vehicle control. All dashboard instrumentation, except for the tachometer, stopped functioning. There were no 'warnings' previous to this failure. After shutting the engine down then restarting, the engine and transmission seem to operate normal. Have taken vehicle...