power loss in my 300D

[joshyoder]

I've been having a weird power loss issue with my '83 300D. The car runs fine for the first 5 miles, then slows down to about 55 mph. Pushing the accelerator in doesn't make any difference. A few months ago I decided the problem was a leaky vacuum line messing with the wastegate; so I replaced some rubber lines that looked really bad. This fixed the problem for about a month but now it's even worse. I know the fuel tank is venting properly; and the fuel filter is new.