Vibes.

My 200tdi has a vibration feeling appears to come mainly below driving position although some can be felt other areas. Done most of the obvious things, Prop ujs, Brake disc, Wheel balance. Worst at around 50mph then if I dip the clutch and coast runs silent silky smooth would not think I was in a Landy, Soon as I bring back the power its back again and driving me nuts. It was not like it when I bought it could I have got wrong spline position when doing uj as there was no marks. Engine is a good runner for an oldie with plenty of power as I thought perhaps it was motor trouble.
Anyway completely run out of ideas now. Any suggestions as I dont want to part with the old girl. The Disco that is not the Missus.