5.0 lx just a little tweak n peak

i just got this 93 lx 5.0, the guy b4 me installed a cobra intake, bbk cold air, bbk shorty headers to H pipe going back to flowmaster... i am having some vacuum problems that i know for sure so what is the best way starting from scratch to fix this vacuum issue, i have read up on alot of forums and thins to do to use the pre-existing vacuum system and i really cant seem to get it to work properly... the issue its causing is when i step on the gas a hissing/woosh sound is coming from the intake.. i have already checked the MAF air filter ect.. any ideas?? really could use some thanks...