Brake problem

My first guess is stickng pins or hoses, but you got those. Proportioning valve sticking.

“I was a couple more bad calipers away from replacing hard brake lines and buying a master cylinder lol”

Calipers are one of the things I only buy OEM.

OP, many years ago a couple of friends of mine became unemployed when the company they worked for shut down. This was a large warehouse distribution center.
Both of them went to work for Fred Jones Manufacturing in OK City; a huge operation that provided reman parts to Ford dealers nationwide and even some GM dealers.

Both of them are great guys to know but neither one of them know one thing about cars and neither one cares to know anything. They don’t even change their own oil.
One of them was rebuilding water pumps and the other (shudder…) was in the section rebuilding carburetors and throttle bodies.

There used to be a large reman facility in OKC called Unit Parts and some shaky products came out of that place. I’ve seen carburetors right out of the box that had no floats or needle/seat and water pumps with the wrong pulley hubs installed.
Guess if that stuff is rolling down the line and the time allotment clock is ticking the main job will be to get the part off the line no matter if it’s right or not.

Wonder how much those battery packs cost…