I'm having a similar issue with my 300sd in the 2-3 & 3-4 gear change. Although I plan on changing the ATF & filter tommorow, I begining to suspect the modulator since it happens only during the first few miles of driving when the outside temp is below 30 (in my humble experience that seems to be when vacuum problems get worse). Just curious if your tranny issue seemed to make it self known as the temp dropped.
1980 Mercedes 240D
1982 Mercedes 300SD
1985 Mercedes 300D
1993 Dodge Cummins Turbo Diesel