Mercedes Benz repair: Tranmission, transmission flush, td class

Question
I just bought an 89 300E AT w/ OD.  It has only 83K miles and drove fine when I bought it.  I took it on a freeway trip aboput a week later and it started falling out of OD when I let up on the throttle.  It was not an issue when I test drove it, although it shift a little rough into 3rd, but not crazy.  Am I looking at an overhaul or do you have any checklist suggestions?

Answer
where you hauling something on the freeway trip overdrive is useful only when hauling, otherwise if you keep it on will ruin your transmission. I would do a transmission flush and filter change, then you may have to get the rebuilt kit for the overdrive check out this post
http://www.benzworld.org/forums/w124-e-ce-d-td-class/1225203-summer-time-tranny-...