general problems of the 2011 Cadillac STS

We own a 2011 Cadillac Sts. Recently my wife was leaving for work and all of a sudden I felt the house shake. My wife was reversing out of the driveway when she applied the brakes. The pedal was so hard she could not press the pedal down. To avoid a crash she put the car into drive to keep it from going into the street. Once she was able to keep the vehicle out of the street she put the car in neutral, but the brakes were still not responding. Thats when our home became our car stopper. I drove the car afterwards and the brake pedal was still hard and would not hold the car from moving when it was put into gear. I contacted the local dealership who informed me that it would take at least 3 to 4 hours labor to diagnose the problem. That at $149. 99 per hour. He also informed me that they had a vehicle in earlier saying the same thing and they pretty much replaced all of the braking system on the car at the cost of over $3900. 00. That is crazy to me so I went through the car myself. I replaced all brakes and rotors, replaced the brake fluid and bleed the whole brake system. All that for the next day the same thing happened. I have since traced the electrical side and have found that the vacuum brake assist fuse under the hood was blown. I have replaced the fuse but as soon as you hit the brake it blows the fuse again.