I wish someone would explain the problem with differential speed to our lawmakers. I am not a commercial truck driver but I believe that having lower speed limits for them creates more problems than it solves.
Truck differential speeds is one reason that I am looking forward to the Tesla semi. The Tesla semi has enough power to pull the vast majority of hills at whatever speed the cruise control is set on and with regenerative breaking speeding going downhill has no benefit as the energy can be saved by other means.