General Motors Co. (NYSE:GM), North America’s largest automaker, announced Tuesday that it sold 187,195 cars and light trucks in July, an 11 percent decline from last year and 32 percent down from August. September saw the lowest monthly volume for GM, while Ford Motors Co. (NYSE:F) saw sales rise 6 percent to 185,146 units, almost tying with the traditionally uncontested leader. At least part of the issue is that GM is grappling to meet demand for its top-selling, newly designed Silverado pickup and its best-selling GMC, the Sierra pickup.

But this decline is temporary. GM is working on the supply issue for its important trucks and is releasing some new products.

"September may have shown a decrease from last year's strong September, but there are silver linings in this story,” said Jessica Caldwell, senior analyst for auto information and pricing provider “Chevrolet dealers saw their first shipments of the highly anticipated Corvette Stingray and inventory is growing for the new 2014 trucks. GM is certainly giving consumers diverse reasons to check out its current offerings.”

Chevrolet saw the biggest drop, of 14.7 percent to 127,785 units, largely on weak sales for the Cruze compact sedan (down 51 percent to 12,730) and the Impala full-sized sedan (down 25 percent to 11,462).

GMC fell nearly 10 percent, pushed down in large part by a 4.6 percent drop in deliveries for the Terrian midsize crossover.

On the other hand, Cadillac was up 10 percent on a rocket rise of its new ATS compact luxury car, to 2,739 units, and a 2.4 percent bump to its XTS full-sized luxury sedan, to 2,565. Buick’s new Encore subcompact SUV helped float Buick by 6.5 percent while the four other models in the brand – the Enclave, LaCrosse, Regal and Verano – retreated.

Click here to read how Chrysler Group LLC fared in September.

Click here to read how Volkswagen fared. 

Click here for Ford.