If everything else looks good, the metal shavings are most likely from the clutch packs. They are expendable parts and normally start to deteriorate at 60K miles, less if the correct additive is not used. I had the same shavings in my used 90K+ mile D44 w. TrakLoc before rebuild/gear change and replaced the clutch packs. There is now an "aggressive" clutch pack kit (Dana Part #: 22937X) that's supposed to last longer, but I have no experience with it. Might be worth checking out since you'll need a new kit anyhow, si?