Retail sales of Ford's F-150 pickup rose 31% in September. After months of shortages, Ford's two truck factories are finally catching up to high consumer demand. Image source: Ford Motor Company.

Ford (NYSE:F) is still working on getting full supplies of F-150 pickups to its dealers and commercial customers.

But you wouldn't know it from Ford's sales results in September.

The Blue Oval said on Thursday that overall sales of its F-Series pickup line, which includes the F-150 and its Super Duty siblings, rose 16% in September. 

That's a big gain that outpaced those of Ford's key pickup rivals. It's welcome news for Ford investors, who know that strong pickup sales usually mean Ford will report strong profits

The big gain was driven by a 31% gain in retail sales for Ford's F-150. That's especially good news: Customer demand continues to be very strong for Ford's aluminum-bodied trucks, and Ford's dealers finally have lots of the new trucks to sell.

Supplies of the new F-150 are finally catching up to demand
With 69,651 F-Series trucks sold, it was the best September for Ford's full-size truck line since 2006. Sales just missed topping the 70,000 monthly mark for the second month in a row -- but I don't think Ford executives were too disappointed by the results.

For much of the year, Ford struggled to post sales increases with its top-selling truck line. That wasn't because the market was sluggish -- in fact, demand for pickups in the United States has been extremely strong for a while now. 

It's because supplies of the F-150 were exceptionally tight in the months following the changeover to the all-new 2015 model. Both of Ford's truck factories had to be shut down for weeks in order to retool to make the new aluminum-bodied trucks. Those factories normally run at full speed nearly around the clock. The shutdowns left dealers with thin supplies for a long time.

Now that both factories have been up to speed for a few months, Ford is close to having what it considers to be normal inventories of the F-150. But the two factories are still racing against very strong customer demand -- a good problem for the Blue Oval to have.

Ford is starting to win back some commercial sales from GM
Ford's U.S. sales chief, Mark LaNeve, said on Thursday that the company started September with about 92,000 F-150s in inventory and ended the month with about 100,000. Its ideal number is probably around 120,000, so supplies are still a little tight, and I've heard from some Ford dealers who are still struggling to get enough of the specific truck models their customers want.

That's not unsurprising given the production disruptions and the high demand for the new F-150. But as a group, Ford dealers clearly had enough trucks to generate a great sales month -- and Ford's factories are able stay a little bit ahead of demand.

While retail inventories and sales are close to what Ford wants, Ford is still working to catch up on the commercial-fleet front. Sales to companies that operate fleets of trucks (like big contractors, mining companies, oilfield-services companies, and even cable-TV companies) are an important part of the pickup market in the United States. 

A lot of F-150s are sold to commercial customers. As supplies get close to normal, Ford is making more F-150s available for commercial-fleet sales. Image source: Ford Motor Company.

Sales to rental-car fleets aren't always a good thing, but these commercial fleet sales are good, profitable business. Ford and General Motors (NYSE:GM) compete hard for it, and Fiat Chrysler would like to get more of it.

So far in 2015, GM has been the big winner on the commercial-fleet front, at least when it comes to pickup trucks. That's partly because GM has made a big push to expand its commercial fleet sales with a strong pickup line of its own. But it's also partly because while F-150 supplies were tight, Ford chose to prioritize deliveries to retail customers over its fleet sales.

Ford has been making more commercial-fleet deliveries as its inventories have neared a comfortable level. LaNeve said that about 17% of F-Series sales in September went to commercial-fleet customers. 

That's still a little short: Typically, in any given month, commercial-fleet sales represent around 20% of total F-Series sales. But again, it's another sign that Ford's truck inventories and truck sales are close to "back to normal."

Next up: an all-new Super Duty
The next big wrinkle for Ford's pickup business will be the introduction of an all-new Super Duty line. Like the 2015 F-150, the 2017 Super Duty trucks will have aluminum body panels. They'll also have other changes intended to make them more durable and improve their towing and hauling capabilities, as well as a long list of new high-tech features. 

The all-new Ford Super Duty with aluminum body panels will arrive at dealers in about a year. Image source: Ford Motor Company.

Ford expects the new Super Duty models to start arriving at dealers in about a year. The good news is that -- unlike Ford's F-150 factories -- the Kentucky factory that makes the Super Duty trucks won't require extensive downtime to switch over to manufacturing the new models, LaNeve said.

But in the meantime, it looks like Ford is finally hitting its stride with its new F-150.

John Rosevear owns shares of Ford and 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.