The major factors for the change in net sales and revenues, cost of sales and revenues, and gross margin between  2010 and 2009 follow:  •   The higher truck delivery volume reflects improved market demand which also resulted in an increase of $523.1  million from higher average truck sales prices.  •   In addition, there was an increase in cost of sales of $256.5 million due to a higher average cost per truck,  primarily from the effect of higher content EPA 2010 emission vehicles in the U.S. and Canada.  •   Factory overhead, warehouse and other indirect costs increased $89.7 million primarily due to higher supplies  and maintenance ($38.6 million) and salaries and related costs ($16.5 million) to support higher production  levels.  •   Higher market demand also improved aftermarket parts sales volume by $266.7 million and related cost of sales  by $176.0 million.  •   Average aftermarket parts sales prices increased by $51.3 million reflecting improved price realization.  •   The currency translation effect on sales and cost of sales was not significant as a weaker euro and British pound  was offset by stronger Canadian and Australian dollars. * Percentage not meaningful Net sales and revenues and gross margins for truck units and aftermarket parts are summarized below. The  aftermarket parts gross margin includes direct revenues and costs, but excludes certain truck costs. NET  COST  GROSS  ($ in millions) SALES  OF SALES  MARGIN 2009 $ 6,994.0  $ 6,414.9  $ 579.1 Increase (decrease)  Truck delivery volume 1,410.7 1,189.3 221.4 Average truck sales prices 523.1 523.1 Average per truck material, labor, and other direct costs  256.5 (256.5) Factory overhead, warehouse and other indirect costs  89.7 (89.7) Aftermarket parts volume  266.7 176.0 90.7 Average aftermarket parts sales prices  51.3 51.3 Average aftermarket parts direct costs  12.5 (12.5) Currency translation  (8.5) (13.4) 4.9 Total increase 2,243.3 1,710.6 532.7 2010  $ 9,237.3  $ 8,125.5  $1,111.8 ($ in millions) Year ended December 31, 2010 2009 %  CHANGE Truck net sales and revenues: Trucks  $ 7,042.9  $ 5,103.3 38 Aftermarket parts  2,194.4  1,890.7 16 $ 9,237.3  $ 6,994.0 32 Gross margin: Trucks  $  366.1  $  (46.6) * Aftermarket parts  745.7 625.7 19 $ 1,111.8  $  579.1 92 Gross margin %: Trucks  5.2% (.9)% Aftermarket parts  34.0% 33.1 % 12.0% 8.3 %