You need to make sure you have the correct modulator pressure first.
Call Mercedes with your tranny number...stamped on body just above pan gasket.
It sound like you have too much vacume to the modulator at small throttle openings and incorrect at other positions.
The vacume to the transmission is infinitely adjustable at the i/p as long as the correct restrictors are at the vac' ports and the throttle control on the i/p is operating....along with correct lay out of vac' hoses too.
Steve at Continental Imports in Florida has a blow by blow 'How To' on this system.
Here's the link.
http://www.continentalimports.com/ser_ic20242.html
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