...if you can reach down there, take off the BOV (search there is a how to on the Dejon spring install that you can follow for removing it) and check the spring and rubber diaphragm. I would think the BOV is shot or possibly wastegate/solenoid could cause these symptoms. But I know for a fact the BOV is crap...have gone through 3 so far.

If the turbo was going, you would hear the bearings wine/grind....Mine went at 8K, so I know the sound. On the otherhand, maybe the turbo is cracked....causing these intermittent issues, but the over-boost doesn't make sense then.

 

I agree with "Jeramie JJ". If you feel it "sputtering" at WOT high rpm, it's either a waste gate or waste gate controller which is inconsistent causing varying levels of boost. It also could be knock retard being enabled because of detonation at 21 psi boost. And, of course, it could be misfire, as someone else on this thread suggested.

In any event, if you're seeing 21 psi boost from a engine with no mods, I'd address that problem.