During my time 13 Gear manual transmissions on big rigs was common.....now they are automatics.
It did give you something to do and the clutch could become a real. problem in stop and go traffic back ups as the left leg got awfully tired unless you put the gearbox into neutral when coming to a stop.
Once you the truck rolling the !!!!ting could be done without use of the clutch which was left engaged. and was only used in starting and stopping with gear changes being done by use of the !!!!ft lever and Buttons only controlling torque by use of the "Go" pedal.
That technique was known by Drivers as "Floating the Box".