Anyone have ideas of why the tranny on my '87 300D would flare only during the upshift between 2nd and 3rd gear? I hope it's an inexpensive fix because it wasn't that long ago I had the tranny rebuilt.

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1987 Mercedes 300D ~200K (Greasecar & Biodiesel)
1993 Ford F-250 7.3 IDI diesel 165K (Biodiesel)
1996 Thomas/International Bus with DT466 engine