No work on the brakes prior to this problem. I removed the steering box and had it rebuild a few weeks prior to this.

The car sat for the winter and did not have a problem when I started driving it again in March. I noticed the problem after about a month of weekend drives this spring. When trying to stop, the pedal was ok for the first half, then it gets really firm. I replaced the booster with a new unit. I have quicker and more responce after the swap but about halfway down the pedal gets firm. I can lock up the fronts if I stand on it.

It doesn't have linear braking since this problem began. And seems to not quickly release the brakes after a quick, hard, application of the brakes. It might be two issues, 1 being the none linear braking and 2 the slow release.
Thanks.