Hey guys, I'm having trouble sourcing what seems to be a boost leak during the operation of the Secondary turbos [4500 rpm]. I've already conducted the autosportracetech boost test and I found that my Primary turbos are working fine -- boosts up to 10 PSI no problem -- but I've noticed that when I pass the 4500 RPM mark, right when the second turbos are suppose to kick in, the boost gradually goes down and nets less than 5PSI; it is also accompanied by loud whoosh (no, not the BOV) when the throttle is let off.

Can someone help me source this problem ? I've tried the majority of troubleshooting procedures on the autosportracetech site , and I'm stumped. Some say I need new spark plugs ? But I don't know, maybe, it's worth a try.