Brake Master Cylinder problems of the 2016 Ford E-150

I agreed to purchase this f150 on 1/27/2016 but requested that the mushy brakes be repaired first (pedal goes to floor). Went back to dealer 1/27 to complete paperwork and pick up repaired truck. Was told that the truck was checked by the service dept. And that brakes were normal. I completed the paperwork but left the truck there to be checked by the service dept. Again the next morning. I got a phone call the next morning saying the brakes had been fixed and the truck was ready for pickup. When I arrived at the dealership I went to the truck and pressed the brake pedal and it went to the floor. I was told that it had been checked by four service techs and all agreed that the brakes were fine. They also gave me a service report saying the brake operation was normal. I took the truck home that afternoon since it didn't appear that this service dept was not qualified . On 1/31 I took the truck to a different dealer. They said the master cylinder was by-passing and ordered a new one. It came in the next day and I took the truck in for repair. After the truck was "repaired" I got in the truck to head back home. The brake pedal went to the floor. I went back in and reported that it was the same as before. After discussions, the service dept got a new truck off of the sales lot and showed me that this break pedal also went to the floor, so this pedal operation was normal. I took my truck and returned home. Now I have a very expensive truck that I am afraid to drive. After an internet search for mushy brakes I find that there are many other owners with the same problem. I called myford and told there were no other reports on this. They suggested taking the truck to another dealership. This third dealer said they would have to keep the truck for 5 days before they could even look at it. I did not leave it. Myford then suggested a 4th dealer. Haven't been there yet.