No idea here Tim.

Sounds like DMFW to me though.
If it only happens while moving, then its his carrier bearing.

Luk clutches are not bad for gassers, not sure about on diesels.

 

I would bet DMF as well. Although when my first one went out it would also vibrate at idle a bit. Hard to feel it but it was there. Carrier could also be it too.

I doubt you are interested but I have a new in box clutch and PP kit for a DMF and a slightly used DMF.

 

the carrier bearing is easy to check, just roll under the truck and grab the shaft!