The contact owns a 2013 Ford F-150. The contact stated while towing an empty horse trailer at 65 MPH, the vehicle downshifted into second gear, and the engine revved abnormally. The contact stated that there was a knocking sound coming from the engine compartment. The vehicle was turned off and towed to the residence. The vehicle was not yet diagnosed or repaired. The manufacturer was not made aware of the failure. The failure mileage was approximately 203,000.