Ditto the advice on the OVP relay...those can lead to a ton of nasty symptoms when they get twitchy. Also have you checked your thermostat? Could be sticky/not opening all the way. Sometimes the simple things cause the biggest headaches.

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Current:
1980 300D "Blush"
1985 300TDT "Walter"
1995 e320 wagon "Sopwith Llama"

Greatly missed:
1985 300TD "R2D2"

Don't really miss much at all:
1983 240D "Dee"