I have searched and have not found anything about the issue I am having, other than a couple of Superduty's. I have a 21 3500 with puck system and just purchased a new B&W RVK3600 5th wheel hitch. The hitch does not sit flat on the pucks and rocks. The hitch on the concrete is flat with no gaps or rocking. All of the Superduty's with this issue it ended up being the truck not the hitch. Has anyone ran into this problem. A shim would correct this issue but there is no mention of shims in the instruction.