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I had that ^^^^ same thought, if the sensor is responding, the passage is obviously not completely plugged. This is a reach, and complete speculation, but MAYBE it's partly restricted, right at the manifold fitting as Shawn described, and the restriction is causing the pressure to read higher (smaller opening == higher pressure maybe?).
I don't think that is the case since it reads more pressure than it should when the truck is not running (even though the same concept did cross my mind)
Also, a restriction wouldn't cause more pressure, it would cause more velocity.... or less volume.
Well I know when mine was completely clogged, the sensor read higher than atmospheric pressure until I unclogged the fitting. But that may have been remaining pressure trapped in the pipe.