boost ??

[2fst4u]

I have a 90 laser RS turbo 14b, 255lph, safc1, removed b-shaft, and boost controler. I am curently running 14psi. everything was working fine(spooled up to 14psi around 4000rpm to red line) but now I am having a problem with staying at 14psi.if I get on the gas the car reaches max boost at 4000 then at about 5000 drops to 10psi and trys to go back to 14?? why is it going to 14psi then droping to 10psi and then try to spool up again to 14???any ideas