Here's a picture of it where you can kind of see what I'm talking about.
I actually have the truck at a body shop now to check the frame. We'll see what they find.Snap some pics of the underneath, where the mounts are. Could be somebody did a homebrew body lift and it's not straight. Or could be a bent frame. Have a body shop you trust check that.
While I'm commenting, I like your wheels. Care to share what brand/size they are? And what size tires are you running? Looks good.