navigating high-grade descents are the wrinkle - truck air brakes seem very finicky. But I think there's no reason why long, sparse, flat freeway sections could not be run by automated cabs relatively soon, for example CA-I5 from Tejon Ranch to Stockton, or the I80 between Chicago outskirts and somewhere in Wyoming.
Truck air brakes are finicky because they are mechanically designed to distribute brake pressure evenly across the wheels in response to one input -- pressure from the driver's foot on the brake pedal. An automated cab could communicate more information: desired speed, tolerance, required stopping distance, and general vehicle stability info, and a microcontroller at each wheel could combine that with sensor info abo…
Of course, there is a lot that could be done, but most of that has one thing in common -- money, for the engineering, manufacturing, original purchase, in-service monitoring, problem detection, problem diagnosis, and repair. Money.