Yea sorry - but no - I sold my Ranger because of this, even if others aren't having the same issue mine was. Maybe its got something to do with the pinion angle I remember reading about here.
I drove the truck another year and ahalf to about 45k miles as I recall, and went back to the dealer with the fluid the dealer installed when the 2nd diff was installed. I asked them to pull the cover and inspect, they didn't feel it was required but I knew the service manager personally so they did, and found that diff was eating itself alive (Spider gear was super chewed up as I recall)
Was it installed wrong? Maybe. Was it just bad luck with two units? Maybe, the truck then sat for about 3 months while I had a loaner EcoBoost Mustang, Ford shipped a replacement diff and didn't pack it very well, it showed up with a smashed speed sensor.
At that point it was wait another unknown amount of time for the fourth differential to come in. So I just sold it to the dealer. I had the truck paid off, thankfully, so I just let it go. My needs had also drastically changed personally that helped reinforce the decision.
I think the Ranger is a fantastic platform, and this isn't something widespread, but I went through my original Diff, the replacement diff (On factory fill fluids) and then was on another wait for a replacement, for the replacement for the replacement.
I was sad to let it go, and I hope it found a good home.