How are you adjusting your timing curve? Is the mass air the only form of tuning you got going? I assume you didn't use a FMU with the Novi 1000 if you had 42lbs inj. before.
The Novi being belt driven was rpm based on its boost. So you could have adjusted timing based on rpms. The turbo being load based on the car needs the timing adjusted based on the rate of boost coming into the car, that being either boost retard or chip.
What are you using for a rev limiter?
When I first finished up my install. I had a similar problem with bucking. AFR read lean but was really so rich it was giving a false lean and foaling the plug terribly causing the bucking in the higher rpms.
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.