Sales of the Chevy Silverado fell almost 10% in September. Photo credit: General Motors Co.

Are General Motors (NYSE:GM) all-new Chevy Silverado and GMC Sierra already starting to fall behind?

That was the question some observers were asking when September's sales numbers were released earlier this week. Ford's (NYSE:F) saw sales of its F-Series pickup line increase by almost 10% in September, and Chrysler's Ram gained over 8% -- but GM's trucks saw a steep year-over-year drop.

What's the story? As Motley Fool industrials analyst Blake Bos and senior auto analyst John Rosevear explain in this video, it's not that GM's new trucks are bad. But Ford and Chrysler have made bold moves to shore up their own sales -- moves that have already led GM to boost incentives on its brand-new pickups.

Fool contributor John Rosevear owns shares of Ford and General Motors. You can connect with him on Twitter at @jrosevearThe Motley Fool recommends Ford and General Motors. The Motley Fool owns shares of Ford. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.