maybe its where leaf connect to shackles ? maybe grease or wd40 that area and see if it stops temporarily. or start isolating exactly which junction is causing it..
you jumped yours or went to the oem bumpstops crunch so it really could be almost anything back there
Im going to let Ford figure it out...its under warranty so they can fix this issue. This squeaking issue has nothing to do with a jump as I have seen several gen 2 trucks that have never been offroad and they squeak.