Not sure what your problem is. Boost should return instantly unless you are shifting way slow and loosing the same amount of rpms each shift. I will assume thats not it.
Maybe The BOV isn't closing back up after opening right away. I run a 50mm Tial BOV and I believe that one if not the biggest out there, and I dont have a problems.
Is the BOV closed at idle?
88lx Conv. 200K mile stock longblock. Trickflow intake, 42lb inj, Pmas protube,TKO500, 3:27, pypes muffs, Pa Racing tubluar K-member, DIY single turbo setup. Summit aluminum rad, Crane Hi-fire ign, subfames, 17" sc saleen's, Saleen ground effects, SCT tune by Dynosport. 380HP 435ftbs.