BMW 3 series 2Litre 6 cyl?

Hello Everyone
Thank you in advance.
I shall start from the begining the car starts first turn of the key, it ticks over well, does not go high or low on the revs, revs stay spot on. When the engine is reving through the gears it seems to be holding back (lack of power) I have have had a new crank sensor fitted, all sensors have been checked and cleaned, am I right in thinking that the vanish unit could be playing up. If so could anyone tell me more about the vanish unit, any other comments or anything that would help me would be very appreciated.

Cheers
Willy Wonka ;-) and co