Have you checked that at full throttle the vacuum control lever is within 0.020" of the pin? What vacuum reading do you get when you Mityvac the vacuum control with the lever 10 mm from the pin? (IIRC factory spec is between 6 to 8 inHg) It sounds like you are getting too much vacuum to the vacuum modulator on the trans. causing the soft early shifts. So you have 2 options increase the modular pressure by screwing in the key under the vacuum cap of the vacuum modulator mount on the trans or decrease the vacuum coming out of vacuum control on the IP. I tuned mine to shift the hardest I can tolerate between the 1-2 shift which minimizes the flaring between the 2-3 shift.

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Bill Reimels
Now down to one:
1972 300SE 3.5 W109 (Euro delivery)