I have a DB 18g with all supporting mods, and a Turboxs FMIC. My boost is set at 18 psi, when I do a long gear pull I hit 18, but it wont stay even at 18,(it shakes around there) then after a little bit it sinks to 15/16 psi and stays steady. If I just step on it and go through all the gears I can't get higher then 15/16 psi. I am not sure whats happening?? Please help!!!