Sales of medium- and heavy-duty trucks in the U.S. rose for the third consecutive month in March, up 20.9%, but still trailed February’s 30% gain, Ward’s data shows.

Class 5 deliveries surged 80.2%, while Class 8 sales rose 38.8%, compared with year-ago. All Class 8 manufacturers posted increases in March, most notably Volvo Truck, up 157.2%. Medium-duty deliveries grew 6.6%, but sales of Class 4 and 7 trucks were down.

Related document: Ward’s U.S. Truck Sales by Weight Class – March 2010

Class 7 sales slipped slightly from like-2010, down 4.4%. Deliveries of year-ago’s segment leader, International, fell 26.9% in the month, allowing Daimler to take over the group’s No.1 spot.

Class 6 sales rose 19.1% in March, with a 22.2% gain in domestically built models canceling out the 61.0% drop in import deliveries. Kenworth posted the biggest increase for Class 6, up 228.7%, while Daimler’s Mitsubishi Fuso suffered the biggest drop, down 64.7%.

Class 5’s 80.2% spike was due to increased deliveries for both Chrysler (+244.3%) and Ford (+163.9%). The two brands more than offset losses at Hino (-96.2%) and Mitsubishi Fuso (-92.1%).

The 67.5% decline in Class 4 sales was the largest in the medium-duty sector, as nearly all brands suffered losses in March.

The lone exception was Isuzu, with deliveries of domestically built models down, but sales of imported trucks up 26.1%. International posted Class 4’s biggest decline, down 96.2%, delivering just 13 units vs. 326 in like-2010.

Through March, sales of medium- and heavy-duty trucks in the U.S. were running 23.0% ahead of year-ago. Both Class 8 and medium-duty segments posted an increase in inventory but a decrease in days’ supply, compared with prior-year.

Class 8 ended the month with 24,923 units, for a 52 days’ supply, compared with year-ago’s 22,885 and 66 days’ supply.

Medium-duty inventory rose to 28,632 units, compared with 27,927 in like-2010. Days’ supply for the segment fell to 62, from 64 year-ago.