The transmission on my 1983 MB 300D (>354,000 miles) changes gears rough.

The car has a lack of power and slowly accelerates. It seems to pull the transmission into the next gear.

My 2000 VW Golf TDI had a similar issue which was resolved by replacing the MAF sensor.

So far on the 300D I have done a valve adjustment, replaced the oil/fuel filters, replaced the transmission vacuum valve levers, replaced the vacuum modulator (green cylinder), and verfied the bango bolt assembly on the ADLA is clean.

This has had little effect.

The car has always been this slow since my purchase - not as a result of any of the changes above.

Any recommendations on what else can be investigated to resolve this?

TIA,

JWJ