My brakes are not working properly. I can be backing up and put my foot on the brake. My truck will keep moving until I apply a lot of pressure on the brake pedal. I can be backing up and my truck will automatically brake and stop moving. I have to cut the truck off, start it back up for it to move. I was in a stand still traffic jam and braking a lot and my truck did stop it keep rolling. Sometimes when I apply the brake it slides.. This is the third time I have put it in the shop. I changed the brakes, brake sensor and replaced tires. I am scared to drive it. My truck is currently in the shop now for the brakes. please help.