brakes fail

Frequently I was experiencing a hard brake pedal while trying to stop. Truck doesn't brake during this event. Mostly happens during low speeds ie. parking, backing, and on slopes and hills. Finally, I took in for service and the dealership found that the master cylinder had an internal leak...

I've got a 2001 GMC Sierra with 145-k miles. I only drive it bad weather, so recently 2000 miles a year was about it. Two months ago I replaced the left rear brake caliper, disk rotor and pads. I had my son help me bleed the brakes in the driveway. With the engine running, I loosened the bleed...