Since the shifting was harsh before you fiddled with anything and now it's slipping, I'd go back and find out what you adjusted to invoke the current behavior. If you have too much vacuum going to the modulator, or if the modulator is misadjusted to compensate for the lack of vacuum previously, you'll have problems.

Get a copy of the FSM and follow the procedure TO THE LETTER on how to set the modulator pressure (it will involve connecting a pressure gauge to a test port on the tranny), then fiddle with vacuum to tune it "just so".

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)