Transmission failure, leaded frame model. Truck down shift from 6th to 1st gear and or locks up in 3rd or 5th gear wonât shift up or down. Going 75mph to 1st gear through the truck into a drift and spin. Avoid cars and side wall on pure luck do low traffic. Had kids in the vehicle at the time. Problem has been reproduced by a ford dealer and private mechanics. Components been replaced and still continue to have problems on the 4th transmission in less then 6 month. By inspected by a mechanic no warning on the down shift no light no indication of failure. Throws a system check light but no other lights and light goes off after truck has been turned off and on a agin.