vacuum leak?

whats happnin everyone? so heres the deal, last night i drove over to a friends house to watch a movie and my car ran fine. This morning when i woke up to drive it home i could not produce any boost. My boost gauge reads 18 (psi?) i guess of vacuum when im at idle but when i get on it the guage goes to zero and then the car almost stalls. When i let of the gas and the vacuum pressure comes back its fine. I just cant get any boost, the engine seems to stall when it hits zero. I dont think my turbo is bad, i have 60,000 miles on my 97' GS-T. I dont know if its in my sig. or not but my mods are, injen intake, greddy intercooler piping, AEM tru-time cams, HKS cam shafts, greddy type s blow off valve that re-circulates and tanabe three inch exhaust. Those are the big things that might make a difference on what it is. Thanks for your help guys.