Vacuum varies with load, not RPM. If you nurse the speed up gradually, with light throttle in neutral, the vacuum stays high. Goose the throttle with the car in gear, especially the higher gears where the engine can't accelerate quickly, and the atmospheric pressure rushing past the open throttle plates just kills any vacuum that's there. Once the speed comes up, and the load stabilizes, the vacuum will go up again.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!