I will relate 2 experiences that may help.
The first involved a tire rotation. After the tire rotation, my wife's truck pulled hard to the right in the right lane on a stretch of highway on her way home from work. Just for about 1 mile. I duplicated this on a side street, rather by accident. No idea why. We replaced the front tires, and the problem went away.
Yesterday, the brakes went out on my Fiero, due to a leaking left rear brake hose. As I got low on fluid, one of the wheels would lock up, but only after 90% of the pedal travel. Nothing happened until after the last 10%, with the pedal basically on the floor. My situation yesterday reminded me of this issue of yours. At the time, the prevailing thought was that it was a bad left rear caliper. Eventually, I crawled up under the car and found out what was happening. My brake fluid was seriously low, with the rwar chamber basically empty.
I wonder if you could have a flow situation. Maybe rather that test weight at the wheels, check fluid pressure at the calipers. Or, maybe it's a tires issue.
