My brake pedal was getting hard so I changed my booster, still no change so I changed the Master cylinder, still no change so I swapped out the proportion valve, still no change. I bleed the system good between each change. Calipers and pads/shoes are all less than 6 months old. I guess I need to drink before I work on it instead of after to figure it out. Any Ideas? I have vacumn on the intake hose but not sure if its enough. The only oddball thing is the (cab) brake booster is 69 1/2 ton chev and master cylinder (frame) is 78 3/4 ton chev. It did work for a couple months just slowly got worse.