In a former life we would put new drums and rotors on the brake lathe. They actually had a little extra material to true them up out of the box. I’m sure the quality of the parts today hasn’t improved. Sounds to me like you’ve got a disc or drum that’s Not true. Only one way to find out and that’s to have them put on a brake lathe to see. Other thing off the top of my head is were the pads and shoes properly bedded after install. This is what comes to my mind. I don’t see how the pushrod would cause a brake pulse during application. Here’s an article on bedding in the frictions and why.
How To Bed In Brakes, How To Break In New Brake Pads
