I have had the car since last June and have been slowly sorting out various issues which includes sorting out the power steering, second battery earth, 5 new wheels and tyres plus new brake discs, pads and shoes and also a bit of pre-emptitive maintenance by having the inlet manifold replaced to minimise the possibility of swirl flap problems. In the recent past I have had a full 90,000 service done and at the same time had a full clutch replacement with new slave cylinder, friction disc and D.M.F. as the bite was very close to the top of of the clutch pedal. All this was done using genuine LR parts and lubricants. When the car went in to have the work done there was no indication of any clutch slip and the car drove very smoothly. A short while after the work had been done I started to feel vibration in 6th at around 60mph when the engine came under any form of additional load. This could have been down to the bedding in process so I was not initially too concerned. When I got the car back the steering wheel was not at dead centre driving in a straight line but this was rectified. Unfortunately over a period of time, the vibration which could be felt through the floor and sometimes the car seat got worse and was apparent through all the gears and across the whole speed range. This was a bit disconcerting as there had been no untoward vibration prior to having it serviced and the clutch done. It was then found that there was some play in the front nearside drive shaft so that was replaced which certainly made the car feel tighter and also a full 4 wheel alignment was carried out. I have had the car back to the Landrover specialist who carried out the work who has stated that that they cannot find anything wrong. I do not want to go into any detail regarding who has done what but I know that there are some very knowledgeable members on this forum and would appreciate any views and or observations that they might have
One further point is that there has been no undue vibration felt through the steering wheel either before or after the work was carried out.

Really not meaning to be rude... but that's much too hard to read in one long paragraph..

Don't worry Paul. W I was able to read it all without problems - and I am not even from UK!

Unfortunately I think the vibrations comes from your new DMF. This is a double flywheel with springs between them to absorb vibrations and make life easier for the gearbox. (I guess you know that.) It seems your new DMF is not a 100% match for your car - even if it is an "original" LR part. (Luke I guess) Maybe the springs in the new DMF are a bit stiffer and have a different resonance area?

The wheel alignment problem is a natural consequence of the clutch replacement too. I guess they have had the whole sub frame off and it is difficult to hit exactly the same place when they bolted it on again. They should have done the wheel alignment before they returned the car back to you!

It is not easy to fix the vibration problem here, if my assumption is right.

Thank you for your response FL2Printzern. What you have said very much echoes my thoughts and yes it is not easy to fix the vibration problem as if it does stem from the new D.M.F, it first has to be proved that it is indeed the D.M.F which is at fault.
The question is how do you do this without stripping the car down again. My initial thoughts are would this be possible by applying vibration sensors with the car mounted on a 4 wheel rolling road.
Another concern as you have rightly pointed out is the effect of continued vibration on other components within the drive train.