[Rich72C10]

Well, it isn't the drive shaft or any of its bits or the rear end. I had it on the rack yesterday and everything is in perfect order. The rear end cover was removed and all checked out - other than the oil needing a well deserved change (the report was it looked like swamp mud). The shop said the rear end bits are in such good shape, that they were pretty sure it couldn't have been original 72 internals. Though I haven't any information any work has ever been done on it but that doesn't mean it hasn't been worked on prior to me getting the truck!

They did find one of the rear wheels being out of balance real bad, which kind of pisses me off as the tires were replaced about two months ago by Discount Tire.

So the good news, rear end is in great shape and I no longer need to worry about the minor cover leak, the state of the oil, drive shaft, or U-Joints/Carrier Bearing.

Bad News, no improvement in the ~40mph noise. So that means it is coming from forward of the drive shaft or I guess the engine / flex plate??