I'd do the fuel filters first. They are cheap and would give many of the symptoms you describe.

Does the transmission shift properly, i.e. at the correct rpms, not too soon?

I just drove an 83 240d auto from Vermont to Ontario and the previous owner said it had no power and would only 25mph up hills. Turns out the engine is sweet, but the auto box gets into top gear by 20mph and therefor has no "get up and go". Manually shifting my car makes it go full speed up hills.

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I choose to be happy, even when the Mercedes is being awkward, lol