when on the frewway or after the car has reached a certain temperature the transmission (automatic) will not shift out of first gear with sufficient transmmision fluid and other fluids water,oil,being full have checked the transmission oil and have add additives to it wich seemed to have solved the problem temporarely but not permernant
transmmission will not get out of 1st gear on 1994 Mercedes-Benz E420
Usually shifting issues are due to electronic faults which cause the transmission system to go into "limp home mode" whenever a serious fault is recorded. Typically the condition will disappear if you shut the car off and restart it and a warning light or check engine light is usually present. So if you can duplicate this you'll know it is an electronic issue rather than a mechanical one, which usually means transmission rebuilt.
I saw this answer and I have the same issue with my 1997 E420. My issues are with the 2 places that have looked at my car. One says ( who is suppose to be a MB expert) it is an electronic sensor. Another shop disagreed with that diagnosis and said they need to drop the transmission and look at it's internal parts. OMG---who do believe?????