Jerking while driving

Hi,

I have a 1.8 turbo diesel. I posted a similar question here earlier but since then I did a lot of work on my car and nothing changed. The problem occurs when in gear and driving, it manifests as a small or sometimes larger jerking or some sort of pulling, its really strange and hard to describe. I literally tried everything and replaced so much parts that 80% of the car is now new. So if you could help me with this one I would be really thankful. The strangest thing is that the car is almost entirely mechanically driven since it has a mechanical injector pump and its not electronically operated as far as the engine goes.

I will list all the things I did on my car so far:

-Replaced Gearbox and entire clutch system, changed gearbox oil too.
-Replaced Timing belt and all of its components that go with the kit, all other drive belts, water pump, coolant changed and all filters (fuel, air and oil).
-Replaced all 4 injectors
-Rebuilt injector fuel pump from the scratch bringing it to its factory condition, timed it also at a licensed mechanical store that deals with these kind of fuel systems.
-Replaced both CV axles and all suspension components (ball joints, tie rod ends. Bushings even)

All in all I did almost all and this problem persists. No vacuum leaks also, nothing.

Sorry for long post but this will bring the situation closer to you.