Rear brakes on 66 dart NOISE and stutter?? HELP

Ok 1966 dddart, 270, sedan slant 6 of course.
I redid all of the brakes about a year ago. it is the original 9in drums all around. This included replacing all cylinders, all pads, all hardware, and new rear Drums.
This issue is not always, but it is often. AFter I have been driving for a few minutes, if I apply brakes to come to a stop or slow down as I get to about 20mph and below I feel a stutter from the rear brakes, like pulsing the car back and forth and I hear rhythmic click that gets slower as the car slows down to a stop. If, as I am slowing and release the pedal, the clicks will stop, but if I press pedal again the clicks and rear car pulse starts again. (pedal is not pulsing, the back of the car is pulsing in time with the clicks).
Any idea what is happening here?
Here is a pic of one of the rear brakes I did back when I replaced everything.

rear brakes - 1.jpg