I seem to be having a similar problem. I believe mine is coming from the steering rag joint ( I think thats what its called, haha. Its the rubber spacer that connects the steering wheel to the rest of the steering shaft). But I think mines going bad because of my body lift. I had to trim the steering shaft spacer a little to fit, and that creates some slop in the rubber joint.
When I drive onroad, there is no play but as soon as I hit a gravel road, its seems loose. I was wondering if the rubber could be replaced with a soft plastic to eliminate some slop. My best guess is that is your problem as well. Its easy to inspect, all you have to do is go under the dash and pull off the steering shaft cover which is held on by 4 little white clips. Hope that helps.