What is your Vin...basically, is yours an earlier truck?
The reason I ask is that...weird as it seems...early trucks (unknown how many like so many other things about these trucks) had a coil spring type thing on the pinion instad of the usual shim setup. This has come up due to a few members in the past tearing into the rear axle and changing gears or investigating howling noises or other problems. I know a guy who found at least 2 different ones this way. He talked to a motor pool veteran in the early 90's and was told that there were these strange setups, they caused problems in service, the militarys equivalent of a recall was done and all of the so equipped trucks were supposed to be refitted with the normal shim type setup.
Obviously some were missed...about a half dozen I know for sure...maybe one more now?
Lord send your Holy Ghost into our hearts and make the desire of our hearts Your Will.
Pro-choice, that's a LIE, babies don't choose to die!!