Yes it does slide back and forth. Both bushings are still there, but I'd be willing to replace them if it would help the problem. I also thought of the washer behind the peg on the right - I thought I would try and actually bring that side of the bed back in. The truck has been in the family for most of its life. We are horse people (at least back home) so it may have had some hay dropped in.

I'm tempted to get a huuuuuuge rubber mallet and start wailing on the corner...

Thanks for the replies guys, keep em coming (please)