You sure it's not the transition from primary turbo to secondary turbo?
Do you have a boost gauge? If not, install that first. Then let us know your boost pattern, i.e. 10-8-10 which it should be if you floor it in 3rd gear from 35 mph.
It should be 10 psi from 3000-4500 rpm, then dip to 8 psi really quick and back to 10 psi until redline. It may start to fall a little as you go to redline.
'94 Montego Base
Current Mods: Street Port (Racing Beat templates), M2 Stage 3 ECU, Stock Twins, Apex'i Power Intakes, DP, MP, HKS Super Dragger II, Greddy TT and Profec B Spec II controller (10 psi Low, 12 psi High), Eibach Pro-Kit Springs, Autometer Boost/Vac guage, Silicone Vacuum Hoses, HKS "style" Circle Earth Grounding
Autometer EGT/Water Temp/Oil Pressure guages, Greddy 2-Row FMIC, Feed Type II spoiler, CF sides, CF rear diffuser, '99 spoiler, '99 bumper lights, '99 side markers