What is the vacuum reading at a steady throttle setting, maybe 2,000 RPM in neutral? If it's under 18 inches of mercury, you've got the timing chain one tooth out of time. A quick way to check this is to take the passenger's side valve cover off and watch the #6 cylinder valves as you turn the engine over slowly. The exhaust valve should be closing, and the intake just starting to open, as the timing mark aligns with top dead center. (0 degrees). I'm going to predict that the intake valve will be open way too far as the TDC mark lines up, from the cam being one tooth late on the timing chain alignment.
Jerry

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