Throughout 2015, General Motors (NYSE:GM) has increased its share of the lucrative U.S. pickup truck market. It was helped by supply constraints at cross-town rival Ford Motor (NYSE:F) early in the year, but even as F-150 supply has improved, GM has remained king of the hill.

In October, this trend continued. Once again, GM gained market share -- not only from Ford, but from every other participant in the U.S. pickup market: Fiat Chrysler (NYSE:FCAU), Toyota Motor (NYSE:TM), and Nissan.

GM racks up another big pickup sales gain
Last month, Chevy Silverado sales rose 10% year over year, building on a similar 10.1% gain a year earlier. While sales of the Silverado's sibling, the GMC Sierra, fell fractionally year over year, total sales of GM's full-size pickups increased 7.1% compared to October 2014.

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Pickup sales have soared at GM in 2015. Image siurce: General Motors.

Meanwhile, combined sales of the Chevy Colorado and GMC Canyon mid-size trucks more than quadrupled, as the two models had just started to reach dealer lots last October. GM has been selling its mid-size trucks at a rate of nearly 10,000 per month this year, which continued in October. Most importantly, it has done so without cannibalizing sales of the more profitable Chevy Silverado and GMC Sierra.

In total, GM delivered 79,642 pickup trucks in the U.S. during October: up 17.7% from the 67,688 trucks it delivered a year earlier.

Competitors can't keep up
Most other major players in the truck market did reasonably well during October, but none could come close to matching the General's strong performance.

Ford has always been GM's biggest rival in the pickup market. GM has definitely benefited this year from supply constraints affecting the Ford F-150 as Ford transitioned to a revolutionary aluminum-based body. But Ford's supply constraints are now easing, and GM remains firmly in the lead in terms of sales volume. F-Series sales totaled 65,500 last month, up 3.3% year over year. Ford also sold 833 heavy trucks -- a segment GM doesn't compete in yet -- in October.

While GM held a comfortable lead over Ford in the full-size pickup market alone, its advantage is even greater because Ford doesn't sell a mid-size truck in the U.S. right now. The Ford Ranger used to cover that market segment. While Ford is reportedly interested in reintroducing the Ranger to the U.S. market, it won't happen for at least a few years.

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Growth has faded in 2015 for Fiat Chrysler's Ram truck lineup. Photo: The Motley Fool

Fiat Chrysler doesn't sell a mid-size truck, either. Meanwhile, its Ram trucks have consistently been a distant third to GM and Ford's full-size pickups in terms of market share.

As recently as last year, Fiat Chrysler was making big sales gains in the truck market through the liberal use of incentives. However, those gains have petered out in 2015. Last month, it sold 40,931 Ram trucks: up just 2.8% from October 2014. That's in line with the full-year trend at Fiat Chrysler.

Among foreign brands, only Toyota sells a meaningful number of trucks in the U.S. In the mid-size truck market, it is quite successful; it sold 15,233 Toyota Tacomas last month, up 17.1% year over year. That put it ahead of even GM. (That said, GM reentered the mid-size truck market just a year ago and is already selling nearly 10,000 Colorados and Canyons each month.)

On the other hand, in the more lucrative full-size truck market, Toyota remains a bit player. Sales of its Toyota Tundra declined 0.1% year over year to 9,514 in October.

Finally, Nissan sells both mid-size and full-size trucks in the U.S., but not very effectively. Both the Frontier and Titan models posted double-digit sales declines last month; deliveries of the two models combined totaled a meager 5,646 units in October.

GM is strong and getting stronger
Tallying up the results, it turns out that GM gained market share against every single competitor in both the full-size and mid-size truck markets during October. Including both categories, the General's market share was nearly 37% last month. It achieved this strong sales performance without resorting to big discounts. GM reported that its incentive spending for full-size pickups declined about $200 both sequentially and year over year.

Finally, General Motors isn't resting on its laurels. It's about to launch refreshed versions of the Silverado and Sierra for the 2016 model year. This comes just two model years after the current-generation Silverado and Sierra were introduced. This is a little faster than most automakers refresh their lineups -- but it shows how committed GM is to sustaining its sales gains and maintaining its No. 1 position in the truck market.

Adam Levine-Weinberg owns shares of General Motors. The Motley Fool recommends Ford and General Motors. 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.