Rear Suspension Shock Absorber problems of the 2005 Ford F-350

2005 Ford F-350 develops sever vibration and the oscillation of the steering wheel causes severe steering difficulty. This problem does not dissipate until speed is reduced to approximately 40 mph. Obviously this is very dangerous on a fast moving freeway where speeds can exceed 70 mph. The condition is addressed in literature program 09l02 letter dated November 2011. The vehicle has been checked after an event and the technician has never discovered a deficiency that he can attribute to this malfunction. The technician has checked all suspension, steering and tire related items. The tires that are on the trucks are load range e tires and are properly inflated to the maximum pressure per the manufacturers (big o) specifications. All suspension and steering part are factory installed or oem parts and the shock absorbers are heavy duty.