98 1500 5.7 vacumn check - internal leak

[jmrich56]

I have a 98 1500 w/5.7 - need to resolve a PO305 -cylinder 5 misfire.
Having checked out the typical suspects - spark, spark plug, plug wire,
distributor cap / rotor, fuel pressure, fuel pressure bleed down, & compression,
2 mechanics suggested an internal vacuum leak. Didn't think to ask how to
perform a check for that. Came home and googled - found a test that makes
sense but would like to confirm. I pulled the air intake hose out of the right bank valve cover and pulled the pcv valve out of left bank valve cover. Started engine and put my thumbs over both valve cover inlets. There was noticeable
vacuum at both valve cover inlets.
Can someone confirm that there should not be vacuum at the valve cover inlets with the pcv hose removed from the valve cover?