...I have a 1987 300D,...that seems to have a throttle pressure shifting issues...
...It stays in each gear way to long and sometimes will not shift into 4th without letting off the throttle...

...On the freeway it sometimes will downshift from 4th to third at freeway speeds without any change in throttle position...

...I do not know if the throttle pressure controlled by vacuum or electronically...and am unsure as to where I should start looking for the problem???...

Thanks