Well, you've checked out the cheap and cheerful fix, so it's time to take it to the MB aware tranny shop and talk valve body. Most likely it's a stuck valve, but could also be a broken accumulator, and this cannot be fixed short of some dissasembly. It can be diagnosed by checking the operating pressures in the tranny by someone who knows how.

This problem has been cured by a valve body replacement on some cars here on the forum, so it's worth checking out. Cheaper than a rebuilt tranny, anyway.

It's most likely either a bad governor or a stuck shift valve, and Trans-X won't do a thing for that.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!