Well took the service writer on a short trip to have him hear what I was hearing in the tranny/rear end. He says that all the trucks have a range of speed at which this whine develops.
Sounds plausible but also sounds like "don't bother us, your warrantee is out in less than 800 miles".
Don't remember hearing it originally or even in the first 30k miles. Only recently.
Input?
Gary