Sales of medium- and heavy-duty trucks in the U.S. rose 10.8% in April vs. year-ago, slightly bettering March’s 10.6% increase to mark the sector’s biggest gain so far in 2010.

Class 8 again shone brightest, with a 29.5% increase, the largest of all groups.

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

Daimler AG’s Freightliner was the leading gainer in Class 8, up 78.1%, while Daimler’s Sterling marque suffered the biggest decline, down 66.7% for the month.

Medium-duty trucks slipped 3.7%, with Classes 4 and 7 down from year-ago.

Class 7 sales fell 16.3% on declines at nearly all the volume manufacturers.

General Motors Co. sales dropped 83%, with 40 units sold in April vs. 235 in like-2009. Sterling took the biggest dip, down 88% on a volume of 10 units.

Class 6 deliveries increased 13.8%, as Freightliner posted a 144% rise on 565 units sold. Sterling recorded the largest decline, down 80%, but Freightliner’s performance, plus a 10% increase at Mitsubishi Fuso, lifted Daimler’s overall sales 98.3% for the month.

Large upticks in deliveries at International Truck and Engine Corp. and Isuzu Motors Ltd. helped lift Class 5 sales up 7.7% last month.

The 325% increase at International, which sold 153 units in April, and Isuzu’s 178.2% hike, offset declines for Sterling (96.2%) and GM’s imported units (82.6%).

International (388.1%) and Isuzu (308.7%) also posted big gains in Class 4 but couldn’t overcome declines at about half the group’s manufacturers, as segment sales fell 12.7%. A 71.4% drop at Ford Motor Co. was Class 4’s largest.

Through April, U.S. big-truck sales are running 8.1% ahead of like-2009, with volume of 68,034 units compared with 62,964 year-ago.

Class 8 inventory fell to 65 days’ supply, or 21,485 units, at the end of April, vs. 97 days’ and 24,791 units year-ago.

Medium-duty stocks dwindled to 88 days’ supply (28,021 units) from 105 days’ (34,760) at the end of April 2009.

In other big-truck news:

• Three-year collective bargaining agreements were inked at three Daimler Trucks North America North Carolina manufacturing plants.

DTNA’s Mt. Holly, Cleveland, and Gastonia, NC, plants are covered by the pacts. Mt. Holly and Cleveland employment will “increase significantly,” Daimler says, albeit with each facility remaining on one shift.

DTNA also says it has more than 10,000 orders for new trucks with its Selective Catalytic Reduction emissions technology. New Freightliner Cascadia, Coronado and M2 business-class medium-duty vehicles offer either Daimler’s Detroit Diesel BlueTec SCR, or Cummins Inc.’s SCR, technology.

• PACCAR Inc.’s Kenworth Truck Co. lands a “major order” from Kansas refrigerated fleet company TransAm Trucking for trucks with its SCR technology.

TransAm Trucking has ordered 1,050 T660s with PACCAR’s MX 2010 engine, which uses SCR in concert with exhaust gas recirculation to meet 2010 diesel-engine emissions regulations in the U.S.

The engine makes 485 hp and 1,650 lb.-ft. (2,237 Nm) of torque.

• Navistar International Corp. will build 400 all-electric trucks at its Elkhart, IN, plant, thanks to a $39 million stimulus from the U.S. Dept. of Energy’s Transportation Electrification Initiative.

The all-electric truck can travel about 100 miles (162 km) before requiring a recharge, Navistar says.

cschweinsberg@wardsauto.com