Johan, first off welcome to bimmerwerkz.
Now, diesel's are notorious for not having much power at lower RPM's, especially turbo diedels, due to the fact that boost is not acheived unti lthe turbo reaches a certain pressure. The only way to get more power is usually by swapping fuel rails, injectors, and larger turbo's into the platform.
best of luck
R.I.P fast 6
Two wheels or Four, I'm happy as long as the throttle is pinned.