Need insight on wierd problem

Did the inside of the coupler have any grooves in it? They do get wear grooves in them sometimes. It sounds like the box or the coupler to me by the symptoms. How is the box mounting bracket? Solid? Did your box come with a warranty? I assume it didn't do this before the box change? Can you get the car up in the air? I would see if there is any movement in the pitman or idler arm at the k frame mounts,up,down side to side.