Brake Drum Wheel Cylinder problems of the 2015 GMC Sierra 1500

I first noticed the problem when I was backing down the ramp to launch my boat. Generally I can lightly touch the brakes and the truck will stop immediately. But this time it did not and I had to pump my brakes multiple times before it finally came to a stop. I was quit alarmed but kinda blew it off. The truck had traveled about six feet further than I had anticipated. About a week later I stopped to go through my gate at my farm and when I drove through the gate which is on a slight hill decline it happened again. I went to touch the brakes to stop and ended up pumping the brakes violently in order to get the truck to stop. This time I traveled about seven or eight feet before coming to a full stop. After this incident I was convinced to take it to the dealership. It occurred once more during that time. The dealership said it was a malfunction in the vacuum pump that works off of the main engine and oil from the engine had contaminated the braking system. I had to have replaced a pump, booster, cylinder, pipe, and fluid for a total of 1266. 33 dollars. That invoice number is 208452. I feel this is a serious safety issue when you think your vehicle is going to stop and it does not. This can cause a panic situation!.

I first noticed the issue on the morning of Saturday, November 10th as I was backing into a parking spot. As I was backing in, I noticed all of a sudden the brake pedal was on the floor and I was about to plow into a curb and threw the truck in park. I didn't think anything of it. The second time it happened was one day later as my fiance and I had just completed a 200 mile drive home. I was pulling into the parking lot at our townhouse complex and as I was pulling forward to back into the space, I noticed I had no braking power whatsoever. I had to throw the truck in park to keep it from hitting a neighbors vehicle. I opened the hood with the engine running, and noticed a ticking noise I hadn't heard before and my brake pedal only had about 1/4" of travel left. I could pull the pedal back to where it is supposed to be but it would just fall back down to the floor. I was able to very slowly and carefully park the truck using park and the parking brake. With the engine still running and the vehicle in park, I depressed what was left of the brake pedal and held it to the floor and heard a moaning noise coming from the area near the master brake cylinder and could feel the brake pedal shuddering under my foot. I feel unsafe driving this vehicle and I was giving no warning of the brake failure. I am having the vehicle towed to sewell Buick GMC in dallas and will update when they find cause. I will also be calling gm customer support as I feel this is a huge safety hazard.