i'd be sure to check the kickdown switch first. i had that happen to me in my 300SD. was driving on freeway, climbing hill. it downshifted on the way up the hill and then wouldn't shift up. next exit i got off and it wouldn't up shift at all. thankfully i was close to home and slowly drove home in first or second gear. bad kickdown switch fixed the problem.

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R Martin
Dallas, TX (Addison)

86 560SEL, 128K