For Starsky's engineering / demo purposes - they could limit themselves to a few safe routes with good connectivity. Just use a couple of cell modems from different networks, maybe add a satellite backup to be extra safe and you should be safe enough if the truck can do basic collision avoidance and lane-keeping.

For the future, the good news is that the world is already headed towards a state where roads come with high-speed connectivity infrastructure for vehicle-to-vehicle, vehicle-to-infrastructure and vehicle-to-x communication. Building reliable, high-speed connectivity to the road makes a lot of sense if you want autonomy to really take off.