Cat C-13 boost leak sound

I have a 2007 t-800 with a acert c-13 that has 160000 on it. Last year on occasions when the turbos would spool up to 20psi, I would have a spuratic boost leak sound and of coarse when i could get my cat mechanic to look at it, it wouldnt do it. Recently I had an exhaust leak fixed. Three broken manifold studs and and slip joint gaskets. Now that boost leak sound is not so spuratic! The exhaust leak must of drone out the noise of the boost leak. The sound I was hearing, I thought was all a part of the exhaust leak. Checked all my bellows and they are fine, no visable cracks on the aftercooler. Is it a possibiltiy that my wastegate valve is hanging open and givin me that boost leak sound. I can barely get 40psi of boost on a good hard pull. This truck used to get almost 50 psi of boost. I dont want to just start throwin parts at this thing and my cat guy is too had to pin down and cant just take it to cat and let it sit there for three of four days for them to find time to look at it. Not to mention with the cost of fuel and the piss poor rates I cant afford to let the dealer handle it. I have to figure this out on my own. Can anybody help me!!!