I need a stepside bed/cab gap measurement?

[rscam]

My rear end is not centered in my wheelwell. Its too far back. I have the bed as far back as it will go. Can someone get me a measurement between the bed an cab? I think my leaf springs are sagging and flatened out which is pushing the rear toward the back. Its just a small thing but it bugs me. All I know to do is unbolt the bed and redrill some holes and move it back.