Have you tried: on the ground, engine off? Is the steering still wonky? If so something in the suspension is binding.
If not the problem is most likely the box. It can't be the pump since that would affect both directions.
Long shot, bad motor mount allowing the header to hit the center link or steering shaft? The engine would be torqueing over when in gear, opposite when backing.

Last edited by ruderunner; 03/29/15 08:38 PM.
Angry white pureblood male