Just to let you guys who are having vibration problems around 1500- 2200 revs know what progress has been made.
I've done the shaft nuts and changed the tyres, reset the engine, gearbox and transfer box mounts (they were all slightly off) and changed out the semi synthetic gearbox and transfer box oil for straightforward EP90. The result is a quiet running machine, except for a small amount of buzz from the transfer box bearing to the front shaft which has to wait for now. Changing the Tyres to an AT pattern from the Heavy MT pattern I use for winter seemed to help oddly enough. Must be something to do with the inertia of the tyres. I'm running my summerweight Kumho 255x75xr15 ventures.
The biggest single improvement came from putting EP90 in the boxes. Next best from the mainshaft nut.
EP90 stays nice and viscous at higher temperatures and soaks up the clatter from the worn gearbox - (150000 miles in my case) so I would recommend that first.
Hope these notes help

Best
Tom