Since you've replaced the VCV and modulator, have you replaced or accidentally removed the various restrictors as well? Those are the little plastic connectors between lengths of hose. They are color coded by ID and the wrong restrictor can have a significant effect on shift quality. Also, are you using the correct VCV? There are at least two versions, one with a blue valve and one with a black valve. The blue valve version passes more vacuum. This is a good document for more info, vacuum tuning starts around page 9:



http://jenniskens.livedsl.nl/technical/Tips/Files/Mercedes%20722.4%20adjustment%20guide.pdf