[Cashburn]

Is the rack square to the frame cross member? I ask because I am aware of a batch of production at some point that had the incorrect orientation of the pillow blocks and the racks were not parallel to the crossmember.

That said if you have truly ruled out the other components (tie rods, ball joints, etc) then you should replace the rack. When replacing suggest a new u-joint assembly at the same time as well as ordering the latest pillow block set since it will angle the rack better for smoother (more even) feel from lock to lock.