380sl automatic transmission - late shifts

[blueshield11]

I have a 380SL from 1983.
I can use some advice about the automatic transmission.
The AT shifts very late into 2nd gear, appr 4000rpm.
I have checked the cable from the AT to the acc. levers and it moves, so it is not stuck. Oil and oilfilter are renewed. I have adjusted the vacuum modulator with 2 turns against the clock, but no difference. Maybe I should adjust more? Or is that not the place to adjust. On forums I have read different stories about the place to adjust the timing of the gear (most topics are about dieselengines). The AT does not slip.

Thanks for any advice