Some adjustments are possible
Check my web site - Cars - Technical - Transmission. While that job if for a 1983 300SD, your tranny s/b similar - though you may have a sliding metal tensioner in lieu of the Bowden cable - similar concept/adjustment.
You may have some luck by tightening the Bowden for earlier shifts and backing off the shift modulator at the tranny a sector or two counterclockwise. The first gets you earlier shifts, the second softens the increased harshness form the first adjustment.
No special tools needed unless you adjust the vacuum range also (reduce it in your case) which means you need a vac gauge, a rubber T connector and some vac hose - <$50 for the lot.
Your tranny is filled to the right level, no?