The contact owns a 2018 Ford F-150. The contact stated that while driving at an undisclosed speed, the transmission independently downshifted into first gear. The vehicle was taken to an independent mechanic, where it was diagnosed with transmission failure. The contact was informed that the transmission needed to be replaced. The vehicle was not repaired. The dealer was made aware of the failure, and an estimate was provided for the cost of the transmission replacement. The manufacturer was made aware of the failure, and a case was filed. The contact was advised to contact the NHTSA Hotline to report the failure. The failure mileage was approximately 122,787.