Vaccum problem ?

I have been having brake issues for a while so i put a new master cyclinder a few weeks ago. It's much better now with the new cyclinder b/c the pedal dosen't float to the floor at lights. Now it seems that the brake pedal is softer at low rpms and you haev to push it aways to get it to stop and at high rpms it is stiffer and is tighter. I was wondering if the vaccum line that comes off the intake and goes to he check valve ( what ever that valve does i don't know) than goes to the power booster. If that line had a hole in it would it cause that type of problem ? Any ideas ? Also i have the rear wheel cyclinders failry tight.

Someone has to know something...

Maybe you should check for airbubbles in the lines.