AWX 1.9PD miss fire from 1800rpm

[Chopperman]

This all started back in November.
I have changed the fuel filter twice. Cleaned the tank pump (that was black and caked). Replaced all 4 injectors. Replaced injector loom. Replaced the turbo. Made certain the inlet manifold is clear which it was.
Good flow of fuel back to the tank.
When I accelerate hard under load in a higher gear, it has a miss fire from 1800 RPM upwards. I have driven it hard taking the revs up beyond 4000rpm to try and clear it.
It will pull and rev fine as long as it's not too excessive.....for a Passat!
It does it from cold.
Disconnecting the MAF makes no difference-still misses.
Disconnecting the MAP makes no difference-still misses.
If it was a petrol, I would have said it was a spark plug breaking down under load.
Fuel flow is very good and holds pressure in the filter.
Put an extra inline fuel pump- no difference.
Temp sender coming Monday but this would only affect when warm not through all the temperatures?
At least it is driveable and my boy can carry on learning in it.
I'd love another PD estate if one was going at a reasonable rate?