dual quad nitrous !!?!!

Vacuum isn't what opens the secondary's, if Velocity. A vacuum gauge won't tell you much on that side.

start in 3d or high gear(light throttle) around 3000 rpm and whack the throttle. stay in it until you hit your shift point.
Loosen air door/s screw 1/2 of a turn and try it again. When it finally bogs off the hit, turn back 1/4 of a turn and test again.

It is vary possible that them air doors are not opening or not all the way.

Good thought JBurch!!!!