While you wait for the Mityvac, you could unplug the vacuum line going from the VCV to the transmission modulator, plug up the fitting where it was plugged in and take it for a test drive. If your shifts get real firm with no flaring, you'll know the problem is in the vacuum 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