Stay focused on the changes you made. As Vikki stated, adjust up your rear shoes. After all, that's where the changes have been made. After that, do a little rolling and braking. Roll back and brake, roll forward and brake. Rolling back and braking adjusts the shoes to their maximum tightness. You say that you have more fluid flow from the new master cylinder so it did need to be replaced. Make sure all your rubber brake hoses are in good shape. That's the other 'usual suspect' for a 'mind boogler'. These hoses can delaminate inside and cause all kinds of strange symptoms.
