Mercedes: Transmission shift, vacuum problem, vacuum system

Question
Hey rob
   My 83 td is not down shifting and sometimes missing
Gears. Reverse is ok and third gear sucks and backing up is fine
But it will not get going. I have replaced the fuel filters and it helped
The power but not the shifting over 1600 rpms.

Answer
Chris,
Sound like you have a vacuum problem with the modulator valve. Could be in  the vacuum pump or you may have a leak in the vacuum system.
Or, you may have a first gear band slipping.
It may be time for a transmission tuneup.
Just be sure that you use the Mercedes recommended fluid. Any other type will probably trash the transmission.
Good Luck
Rob