what does this mean..

My car holds vacuum at idle..steadily around 20. when i rev it up to 3K~ish and i hold, it stays up above 22, and when i 'rev' it goes up, coes down to 0, and climbs straight up to 15...then it slowly climbs up to 20...whats up with that?

the slow climbing, im talking about...what does that imply?

this was all done while the engine was warm. and the needle holds steady...if the piston rings are worn, it shouldnt have 20~ish hhg right? but why does it get lower after i rev it up?

it could be perhaps the system response from dropping from high rpm to a lower idle speed but it could have a leak in the vaccum hoses but then it would never reach that type of numbers

Here's Ickeys link (http://youtube.com/watch?v=Fm1tJhrykfk)

On that note......I'm not sure still, maybe dirty air filter? :dunno:
Or something to do with the cats being "modified"??

Any time you crack the throttle the vacumn should go down. It is possible that your throttle plate is binding up sometimes and sticking partially open. Might check the cable/return spring or for carbon buildup on the throttle body. Things might go back to normal as they settle into place.