Brake help - what am I missing?

[1972Blaze]

I had an issue with not enough braking power (72 Blazer). I checked the whole system out and decided to change the master cylinder which I bench bled before installing. The old one had some obvious leaks inside. I also put new shoes on the rear and had the drums resurfaced. The front pads looked good and I have kept them on for now, although I am concerned that the rotors could be glazed. I changed the fluid (DOT3) throughout the entire system. I bled the wheel cylinders and calipers multiple times at different times just to be thorough. When bleeding the calipers and cylinders the brake pedal had a good range of travel (all the way to the floor) without any issues. I pulled the proportioning valve and did the best I could flushing it out without opening it up. As a side note I also installed a rebuilt booster. It did not change the way the brakes behaved, but it ddid have a tight spot when first pressing the pedal so I took it off and sent it back. I put the original booster on for now.

As of now I have a a little less that 1/4" of free travel in the pedal with a total of about 1.75" of total travel before it bottoms out and feels very hard. When the truck is not running it has a very hard pedal immediately once the vacuum from the booster is released.

The problem is that the truck does not stop really well. If I quickly apply the brakes fully none of the wheels lock up and it travels too far to stop. Even if I am traveling at 20MPH or less it drifts before stopping. I can get a small amount additional braking power if I pump the brakes, but it does not change the overall behavior of the brakes. Once it does stop I can fairly easily pull out from under the brakes with moderate acceleration while fully engaging the brakes.

Is there something I am missing as it regards any adjustments that will allow the master cylinder a longer stroke? There is a small cap nut on the shaft coming from the booster that looks like it could be adjusted a little bit? Maybe I just need to keep trying to work air out of the system? Could this issue be as simple as glazed front rotors? I know most of the stopping power comes from the front, but the back is not locking up either.

Any help is greatly appreciated.

Thanks.