One solution to the slippery metal problem is to get some of those little sticky things that you put in your tub to keep from falling in the shower....
Really, though, the grip tape that they use for skateboards and other non-slip applications could be a solution to the slippery metal problem.
Another thought, as we have discussed in other threads, is to coat the wood with some type of material such as pickup bed liner. The bed liner material is also a great non-slip surface and could be applied to diamond plate as well to give the forklifts better traction.