U.S. sales of Class 8 trucks in April were up 3.6 percent compared with a year ago. A total of 12,315 trucks were sold.
Low-volume maker Western Star, owned by DaimlerChrysler, posted the segment's largest percentage increase, up 114 percent to 184 units.
Freightliner, also owned by DaimlerChrysler, posted a 39 percent increase, selling 4,765 units.
Mack bucked the segment's upward trend, dropping 35.1 percent to 1,228 units. Mack Trucks Inc. is part of the Volvo Group of Gothenburg, Sweden.
International sales also fell, down 20.3 percent to 1,656 units.
Class 8 truck sales for the first four months of the year were down 5.5 percent.
April sales of Class 4 and Class 7 trucks decreased. Class 5 and Class 6 sales rose.