I just purchased my 83 SD this week and it only has 131K. When stepping on the accelerator it takes a few seconds before she actually starts to move. My N/A 300TD takes off quicker to 20 mph. After 20 though this thing gets going.
It also seems to shift very soon into fourth gear. If I decide to manually shift her on hard throttle she shifts into 2nd well (chirps tires), when I shift her into 3rd she will just rev till I let off the accelerator a little and then bangs into gear. When I shift into 4th (D) its hit or miss when she wants to engage. When I floor it regularly sometimes it shifts into 1st in 2 seconds and sometimes not till around 40mph. The 3/4 shift is almost always within a second of each other. When shifting from drive to park it still sound like something is moving or slowing down internally before it park engages. 1-2 seconds.

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Current fleet-
2015 BMW 750i xDrive
2009 BMW 535i xDrive
2004 Chevy Avalanche 4x4
1993 Mercedes 300SD
1993 Mercedes 300SE (parts car)

Previous Benz's-
2001 Mercedes SL500
1983 Mercedes 300SD
1980 Mercedes 300TD
1996 Mercedes E300D
1999 E300DT
1984 300TD-T
1988 Mercedes 560SEL (parts car)
1979 300SD
2003 E500
2004 S430 4Matic
2001 E55
2003 E430