This is a scary situation. I purchased a preowned AT4 Sierra with 4K miles on it. Before I put 1000 miles on it, I switched the front and rear brakes out for the Brembo upgrade. I was riding down the street and heard a sound like I ran over something in the street however I didn’t. No issues until the following day I was backing out of a parking space and no brakes. Brake fluid is full and no appearance as any lines are severed. I’m not taking that truck back until I have a new set of brakes and a full explanation to what happened.