I have a 54 and the step hangers were riveted to the frame. I drilled out the rivets and removed the hangers before the frame went in the bath. I have stood and bounced on the hangers one at a time - very little deflection was noticed - if any - hard to tell exactly because the springs and tires were doing their job. (5/16 cap screws are now used to hold them on instead of rivets)
Why don't you get under the truck and have a look while someone steps on the boards? Maybe some of the rivets have let go.
