I have a very similar issue with a 55 D@DG€. It will idle for eternity, but will loose power and die while driving and then need to be jumped. However only after its well warmed up. And i can keep it from dying if i dont let rpms drop. It has an aftermarket harness. I am 90% sure its the PO installed harness, i just havent had time to get a meter on it.
Happy troubleshooting.
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