Likely a vacuum issues. There is a vacuum modulator on the side of the transmission, the line going to it can have a crack or split, or the rubber boots on the ends of the line may be leaking or failed altogether. A lack of vacuum will cause harsh/abrupt shifts at low speed. You should also check your vacuum lines to/from the VCV on the IP and check your blue UFO (vacuum amplifier) for the same things.

Given this is a diesel, you're a lot better off posting in the Diesel Discussion forum, you'll get a lot more views.

__________________
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!)