Find out what's restricting the exhaust system. You can confirm an exhaust blockage by loosening or disconnecting the exhaust pipe at the manifold. Low vacuum at higher RPM than idle is almost always caused by a plugged exhaust system. I've seen it frequently, so I'm not just guessing.
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!