I had a annoying loss of power issue that was worst when heading uphill or at full load. Took me forever to figure out what the issue was. It turned out to be a damaged and improperly installed vacuum shutoff actuator on the injection pump. Under load the actuator was choking off fuel delivery. Probably not what your issue is, but it is easy to check. Watch the shutoff lever while the engine is running. If it sticks pretty much straight up and does not bob up and down you are probably fine. If it bobs up and down and moves down when the accelerator is pressed then it could be an issue.

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1987 300TD 231,000
#22, afterglow, plastic fan, euro lights, alternator upgrade, cluster housing update