I'm guessing it is the brake booster!
On most power brake boosters there is an adjustment screw/ rod that has to be adjusted to the back of the master cylinder (did you do this?)(Instructions usually come with the booster, specific to the type vehicle)
And the one that "JUST CAN'T BE!" - You may have a Brand New defective booster - yep, it can happen with might near any part you put on your vehicle.
Let us know how it works out.
Saturday, September 10th, 2016 AT 9:56 PM