Well....start up river and work your way down.
While someone turns the steering wheel back and forth, watch the steering shaft joints. Next, watch the input (steering shaft attaches to it) and the output (pitman arm attaches to it) shafts. If there's a delay between input and output, that's a cause. Next, watch both ends of the drag link. Next, both ends of the tie rod. Last, both ends of the track bar. The play is happening for a reason and it will be visually evident.