if it is running without a dead hole, your rings might just be stuck, been there done that, blower motors that spend too much time idling build up a thick carbon like film around the ringlands and then the rings dont seal properly... this is my opinion as you dont seem to have a problem in the lower rpm range... a hole is a hole no matter what rpm ur turning... trust me you'd know if she were dead!!

this of coarse is assuming that breathers are of correct size. I run -8 out of both v/c and a pcv valve in the valley just ahead of the dist... pcv plumbed to breather, valve covers vent to puke tank on my 900scs (10:71 blowers)