sagging coils or twisted frame?

[moodybo]

I have noticed that alot of coil equipped trucks tend to favor a lean to one side! I Really notice this by the unmatched body lines between the bed and the cab. I am shortening my lwb as soon as the weather breaks for warmer. What is a good way to check my frame to make sure it is not twisted instead of just a sagging coil spring? I dont want to cut the frame down to just find out that the bed is off align