[1972 orange c10]

I hope someone here can help me figure my brakes out. My brake pedal has gotten really hard to push since i took my qjet off and put a holley 670 strret avenger. I just thought it was the booster so i replaced the booster and mc and bled the brakes and it was good for a day or so and now its hard again. I took proportioning valve off a parts truck i have and it didnt help. Could the holley be sucking more vacum than the qjet. If anybody could help me i would appreciate and by the way this is a awesome site i get on here everynight and get in trouble for being on computer too long. Thanks morgan