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.
Finally was able to get out to the garage again... With the wheels on the ground and the engine off, the steering seems fine. Really tough in both directions with no noticeable difference side to side. I'm at the point now where I feel confident that the steering box is the problem. So... I'm going to try and lay my hands on another box and swap it in. I'll keep you all updated on whether or not this fixes the issue.
