Td4 engine trouble FIXED!!!

Hi all
Recently bought a Freelander td4 was fine for the first couple of weeks.
Recently on a long run once I hit 70mph the engine felt like it was struggling for power like fuel starvation or a misfire, lost revs down to about 40mph then wouldn’t drive over 40-50 with engine management light on.
When you come off the accelerator and cruise, light goes off and engine sounds fine. Then accelerate again light back on and limited revs...
If the fault isn’t there when I turn the car off will start and drive fine but when parked with fault, it struggles to start (engine light back on and Running like a bag of s@&t
Sometimes clears again and is fine around slow roads.

Any ideas guys??
I’ve changed the fuel filter in the rear wheel arch to make sure this was not blocked.
And tried with both EGR fitted and bypassed.

Fixed
So after replacing inline fuel filter, checking turbo actuator arm was moving freely and swooping egr back on after doing the bypass (incase that stirred up some trouble) I was scratching my head as the fault seemed to be getting worse by the day...
So I had the bonet up and was checking the turbo breather on the back of the engine with the engine running when I leant on the engine cover and the tone changed....
Odd I thought so I done this a few times and the fault came and disappeared. Next I took the cover off the engine to reveal the injectors, and 1 by 1 just pressed the plugs until I found which 1 was causing the tone change.
INJECTOR 2!!!! I removed the plug and low and behold a slight bit of rusty coloured dust, I thought surly not enough to prevent a good contact but a little clean and replaced it and hallelujah...

She runs like a dream...