Brake Abs Warning Light problems of the 2008 Chevrolet Tahoe Hybrid

Started car, put in gear, depressed brake pedal, and it went nearly to the floor. No vacuum assist and the car was very hard to stop even at a rolling speed. The following lights illuminated: check engine light, stabilitrack indicator light, abs warning light, brake system warning light. The following displayed on odomoter screen: service stabilitrack, service traction control, service brakes soon. Vehicle has been at dealership for 2 weeks, with repeated calls to gm engineers, who first recommended replacing the master cylinder, which cost $1000 and did not fix the problem. Since then, the engineers apparently say it is the hybrid brake valve modulator that has failed, which will cost additional $2300; however, the dealer cannot get the part and not sure if this will fix it. This hybrid braking system is defective and dangerous!! I cannot imagine what would have happened had I been driving at full speed. In reading forums, I am not the only one with this issue. I hope the NHTSA reads this with all the recalls and coverups that gm has had to deal with in the past few months. A recall should be issued.