In 2015, Class 8 trucks sales in the US was around 249K and in the NAFTA region, was around 405K (2016).
Truck sales in the U.S. - Class 3-8 2015 | Statistic
Daimler, Volvo are the two biggest. Volvo goes by a few names.
U.S.: class 8 truck market share by manufacturers 2017 | Statistic