Do leaf springs sag?
 

Can the rear leafs sag from having constant weight in the bed? I had sand bags in the back for the winter and I'm kinda wondering if that could cause them to sag and make the rear sit lower without any weight in it.

If this can happen how do I fix it?

Yes, your leaf springs can go bad.

How can you tell if they have gone bad?

If they are sagging bad.

If you look at the leaf springs if they dont have any arc to them and they sit flat they are most likely worn out.

Yeah. Squat down at the rear of the truck and long down along the spring. If it's flat, well... then its shot. When they go flat it makes the rear end stiff and bouncy.