I posted on your other thread yesterday.
Booster and shut off are interconnected. Booster could be bad causing the slow shut off. However, both being bad could be caused by a common problem such as a disconnected line or bad vacuum pump. First step is to visually inspect the main vacuum line going from the pump to the booster. If that looks ok then you'll have to get a Mity Vac and start checking vacuum levels in the system.

__________________
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