Jonnyblond, that sounds like the same problem, just not as bad a case of it. If (or when) the vibration is worse, you can actually hear it as a loud buzzing noise at motorway speeds. It's true that the diesel has a lot of torque (the V6 slightly less) and so in 6th gear and especially if accelerating in 6th there is a lot of force being applied internally in the gearbox - but I don't think we should accept motorway vibration or continuous buzzing as a consequence. Not every car has it so I still think we will find a cure.
There seem now to be six of us in this thread who are experiencing the same problem, plus others who mentioned it in the "play in gear stick" thread (see reference in first post) but none of us has an answer yet, so more posts are welcome please!