Changing the fluid could help if the stuff that's in there has lost its viscosity. As the oil heats up it gets thinner. If the oil is spent it's possible that the viscosity is getting to the point that leakage in the pistons is high enough to cause shift problems.

Also worth checking your vacuum settings. Too much vacuum or a broken VCV will cause shifting problems as well.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

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

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]