i dont think the shut off issue and the ruff idle are related. transmission flare and shut off could be related - vacuum issues/leaks. does your 81 have the idle speed control knob by the instrument cluster ? If so does it affect the idle ? idle issues could be caused by injectors, clogged fuel filters, air leaks in fuel lines.

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1996 E300 110,000
1985 300TD 212,000
1980 300D 238,000