boost killz

Hey guys just wanted to post this because recently the situation has been nagging me. At WOT cars runs great, boost is solid no problem, at partial throttle vacum is at 18(driving miss daisy basically) but at about half throttle with the vaccum reading between 10 and 18 it bounces at increments of 1-3. This occured after a valve adjustment a while back. Any thoughts of why this is occruing and a refference point to start looking at. Thanks,

Nick