These trucks use "hacked up" Pulse Width Modulated DC going back to the trailer connection for the trailer lights. The camera uses the same PWM DC voltage to power your camera.
You can purchase a PWM filter in between your camera and your camera connection. You can get these filters on Amazon for next to nothing.
Also, make sure your camera monitor is not set to cycle between camera's. It needs to be set not to cycle, i.e stay on the same camera without trying to cycle.