vacuum resevoir BIG CAM brake issues

i got a low break pressure at idle and kinda think its caused by my cam and low vacume from it
when car it off and i pump the brakes itgets hard and stays
so i dont think i got a fluid leak fluid is full
has anyone installed a vacuum resevoir to help power breaks with a big cam?
how hard of an install and how did it work out?

well id have to go get the spec card but mechanic said its a pretty aggressive cam and i will have a hard time passing emmissions. im no mechanic by any means. its a comp cam and engine is new with edlebrock performer heads, intake, 70mm throttlebody, 73mm maf, forged pistons, and stuff, 350 hp natural on engine with shorty ceramic headers by bbk
its an 91 auto vert black black. higher torque converter and transgo shift kit. flowmaster exhaust force2. and bad breaks at idle and it runs cold need 180 thermostat