I think my truck bed shifted

[Zakattack7.3]

I turned around the other day to get something out of the back seat and noticed that one end of the toolbox I had in my bed was closer to the window than the other. I thought to myself that was kind of weird. How did my toolbox move? It's bolted down. So I got out of my truck and walked around and the toolbox was flat up against the front of the bed. What I did notice, however, was that the gap between the cab and truck bed was a little wider than usual. I measured it and compared to the other side that looked normal and it the gap on the driver's side was about an inch to half an inch wider than the other side.
I started rocking my bed back and forth but it seemed stable and didn't shift at all. So I don't whats going on.

Has anyone else experienced this problem or have any idea what's going on? I started rocking my bed back and forth but it seemed stable and didn't shift at all.

[SuperCrutyPS]

Do you know if the bed has ever been taken off and maybe not put back on correctly? Check at the wheels. Is one side in or out farther than the other? May have to loosen the bed bolts to adjust it.

Just some thoughts.

[Zakattack7.3]

I know for sure the bed was never taken off and when I get time I'll check to see if one side is sticking out. It's nothing insanely dramatic or anything. You wouldn't even notice it unless you really looked closely at the gap. Just bothers me a lot. I might just loosen those bolts and see if I can re-adjust it then.