After you have followed Wolfe10's advise on how to check for slop in steering components and know that all is well in those components, you can probably adjust the steering box. There are several Freightliner chassis owners on the IRV2 Freightliner forum that have adjusted their steering box. Look at these two threads for additional info
Freightliner steering issueExcess play in steering box freightlinerOn my coach, the adjustment is on the side of the steering gear box, is hard to see, and has a hole in an adjacent frame member to allow access to the steering adjustment.
Fred