There is a bracket on the lower end of the column where the cable attaches that is held on with two torques head screws. Those screws work loose. More than likely that is your prob. Had it happen on my f150 a couple times.
Either that or you need new shaft bushings. They sometimes crack and slide down the tube. There are two that hold the shift mechanism in the steering column. Part number: F3TZ-7L278-A