I have had 2 incidents where my vehicle has suddenly shifted into 1st gear at highway speeds(65-70+mph). I was alone in the vehicle each incident.This caused a sudden and violent loss of speed and nearly locking up the rear wheels, both while entering the freeway. Vehicles behind me had to take evasive action and I had to quickly maneuver to the side of the road. The vehicle operated normally immediately following both incidents. This truck has a 10R80 transmission and has known failures of the CDF drum due to poor construction/quality of internal bushings(pressed in). Ford has since revised this(welded, anti-walk bushing) in newer vehicles but has not addressed the vehicles prior to the revision. I have had no warning lights or codes, nor any other indications this issue was occurring. This vehicle has been maintained well and all services/intervals performed at Ford service departments. I have an appointment in the coming weeks with a local Ford service department for a diagnostic check. The service rep advised based on details I have provided I have CDF failure. This issue has a cascading effect and may require full transmission replacement to rectify. All warranties have expired, repair costs can exceed 30% of current vehicle value.