1998 Chevy Cheyenne Rear brake and flashers

I have lost the brake, signal and emergency flashers on the back of my 1998 chevy truck. It all stopped working at the same time. I checked the brake relay, the fuses in the cab and under the hood and the bulbs. The tail lights work and the reverse lights work. The front lights work, and when you use the signal lights they flash fast, as if the bulbs were blown. could you please suggest something I could check next