without engaging the kickdown feature, what happens when you acclerate to over eighty mph. is there any hesitation?

Is the check engine light on?

these were similar to the symptoms on my 1998 C230 when my MAA mass airflow sensor went bad, what you described plus the high speed hesitation.

go to an AUTOZONE and have the OBDII codes rear if you get something like 0170 it may be the MAA.

Also it is time to have your transmission fluid changed.

Do a search on 722.6 transmission or on the early C230 trans, there have been some upgrades. But do what I said about the codes first.

nice car