Power Assist Brake problems of the 2005 GMC Sierra

Purchased 2005 new GMC Sierra crew cab, 349 miles, on 19 July 2005 from ranz motor CO. , inc. , chanute, KS, VIN 2gtek13t951304774. On 8/21/05 the vehicle began to shake violently, the front brakes locked up, there was a distinct odor emitting from the vehicle, and smoke was rolling out from under the right front side of the truck. Ranz motors replaced a bad brake booster in accordance with bulletin epit3685 and checked operation. On 9/1/05 the vehicle displayed the same defect as described above. This time care was taken to coast to a slow speed before exiting the highway by my husband, a 27 year retired police lt, when the brakes were applied, the steering shook so violently, the steering wheel was jerked from both hands, the vehicle crossed the center line into oncoming traffic narrowly avoiding a head-on accident. Slowly drove the vehicle back to ranz motors (approximately 50 miles round trip). The vehicle was not repaired at that time, but the next day a service tech drove the vehicle only . 21 miles before the vehicle again exhibited the same defect. The tech pulled up on the brake pedal and vibration stopped (ref: case 8421015). Another booster was installed, vehicle was road tested 295 miles without any duplication of previous problem. I have lost all confidence in the vehicle, it's use is not only as a family vehicle, but is also used to pull a 4 horse trailer. No old parts where shown to either myself or my husband either time. I've discussed with ranz motors trading the vehicle back in on something else and steve ranz "wasn't comfortable selling that vehicle to someone else with it's history of problems". Other dealers have depreciated the vehicle substantially based on it's repair history. I proceeded with the GMC buy back program where I was offered $794. 00 and an extended warranty, and told if it happens again we will consider buying it back. I don't like playing russian roulette with my life or that of my family.