When I apply the brakes (factory power disk) the first part of the pedal travel is ok but about halfway down the pedal becomes really firm and braking continues but only if you stand on the pedal. I replaced the booster thinking it was vacuum related since it seemed worse when there was low engine vacuum. The new booster gives more boost immediately but the same pedal firmness (and poor braking) continues as before, but now it also feels like the pedal is taking longer to return to the resting position and the brakes drag for a second or two after you release the brakes.

I hate to continue replacing parts but does this sound like a master cylinder, proportioning valve, or metering valve? From experience I’ve had master cylinders go bad but those had no pedal for the first half, then braking after half way.

I'm planning on doing the PowerTour in two weeks and need to fix this prior.
Thank you.