I can officially state that using Liqui Moly Diesel Clean & Boost

has made my engine run much smoother. The rev fluctuation has mostly disappeared. I did use a huge lot more than what they tell you to use. I'm going to change the fuel filter in the next few days.
I still can't get to the bottom of those revs jumping up and down while driving. I've even noticed since yesterday that my gearbox has been very clucky when changing into 3rd from 4th and into 5th from 4th. Try giving yours a bit of liqui moly diesel clean & boost and see what happens.