[thstone]

Your car has the original Variocam which works via a solenoid which changes the tension on the timing chain to alter the valve timing to give more power at high RPM. As such, it is either on or off based on a pre-set RPM controlled by the DME.

Your problem could be Variocam related but high RPM drivability can also be fuel related (fuel filter, fuel pump, or injectors not flowing enough fuel at high RPM).