Random fast pumping of the brake pedal when stopping

That is called "false activation" of the ABS system. GM has had a real big problem with their front-wheel-drive front wheel bearings developing a little normal slop in as little as 15,000 miles. The built-in wheel speed sensors develop rather wimpy signals to start with. Add that slop in the bearing, and the signal can drop to such a low level, the computer cannot read it, and it thinks that wheel stopped rotating.

To identify this, watch the wheel speeds on a scanner, during a test-drive. You will see one of them drop to 0 mph when the activation occurs. That typically occurs below about 20 mph.

Replace the wheel bearings. If you save them, they can be used on a different car that doesn't have anti-lock brakes.