I'm not really familiar with the vacuum on that year of car, but in the 123's both problems would be caused by a vacuum leak. It's more likely that the leak is in the climate control than in the transmission system since there are more places the leak can occur in the climate control. If you plug the line that goes to the climate control and your shifting improves, you've probably narrowed down the problem to something in the climate control system.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13