Did you make the adjustments to the box by the book?
The tolerance for gear tooth fit change over the length of the screw. In the center they are tight so there is no slack so no wander when the wheels are straight. There is more "slop" when you get off center so turning to the locks are easier.
When the wheels are centered there is a small amount of steering wheel play, a full turn left or right there will be twice as much free play.
That's why turning the jacked up wheels by hand takes a substantial push to get them started, but then moves easily to full lock.