The FMIC should not cause that much of a change in fueling UNLESS you have a boost leak, which it sounds like you do. That would cause an extrememly rich condition. I would go through and check all your couplers and connections first. What map are you using right now? You should not need a boost cut defender, and we really do not recommend using those as they under-report airflow which can cause other issues. We do have FMIC maps for the MS3.
Travis
COBB Tuning