Not sure if you thought of or checked this stuff but I will mention it any way. I know you checked the upper to lower gasket for a leak, but what about the lower intake gaskets. It happened to me before, it was drawing air from the lifter valley because of a bad gasket. You would think if that were the case your plugs readings would not be the same but they were.
I'm not trying to insult you by saying this one, but there is a huge vacum port on the bottom of the upper intake for the PVC. the hose may of sliped off during the installation.
5' of vacum is way to low it has to be getting air from someware.
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347 W/ A-trim 6#'s, Canfield heads, out of the box Systemax II intake, solid roller cam. 11.1 @123mph 1.46 60FT
93lx 5.0 daily driver
MY CAR
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