Major bump

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Here is my problem...I unhooked my powerbrakes when I went with a sbc..I just the pulled hose because the pedal pressure was not consistant. When I was braking the pedal stayed consistant until a certain point in pedal travel then would go soft for about an 1". The problem was when it did this the stopping power would not fad resulting in a sudden increase in brake pressure and a sudden stop. After the pedal pressure would fad for the inch or so the pedal pressure would come back.
I just installed a cannister and guage. Still does it. But I have noticed it does it when there is about 10-11 inches of vacuum and regains pedal pressure at around 7-8 inches. The stopping power is unaffected but its quite annoying while driving on the street. Is this the brake booster or something else? Also I see in this thread that some are using a different master. Do they provide the stopping power of the of the boosted stock brakes?
Also I do hear a SLIGHT squeak when this happens. But if the booster was leaking why would it only do it at 10'' of vacuum?
Now if I need a booster where is the best place to get one?