The contact owns a 2018 Lincoln Navigator. The contact stated that while driving at an undisclosed speed, the vehicle lost motive power. The vehicle lunged forward. Additionally, the contact stated that the vehicle was shifting roughly. The contact stated that the vehicle would redline. There were no warning lights illuminated. The vehicle was taken to the local dealer, where it was determined that a transmission flush was needed. The vehicle was repaired, but the failure recurred. The vehicle was taken back to the same local dealer, who was unable to determine the cause of the failure. The manufacturer was contacted, but no additional assistance was provided. The failure mileage was approximately 86,000.