Sam I don’t know if you have done this yet, but the number 8 runner of the intake manifold below the bolt boss has a bad pinch in on the roof creating a bad restriction.
Grind that all the hell out of there if you have not done so and if you need to use that boss then put sealer on it.
Where you come from is gone; where you thought you were going to, weren't never there; and where you are ain't no good unless you can get away from it.
Ministry - Jesus Built My Hotrod