Yukon Brake Equalization?

[pwsigmund]

My 02 Yukon brakes have gotten progressively worse, even though I changed pads and rotors a year ago. Today I decided to change the calipers, only to find the front pads almost new, and the rears virtually down to the metal. Is there front/rear equalization in the master cylinder, or is there a separate unit? Is that a tricky replacement?

 

Would appreciate suggestions.