The F-150 had a middling year in 2014, and its sales dipped slightly as Ford transitioned to producing the all-new truck with an aluminum body. But with one factory humming, another on the way and a fuller stock of trucks, 2015 is already shaping up to be a different story.

The F-Series posted a 17-percent leap in January, helping to push Ford sales to a 15-percent gain for the month. The F-Series had its best January performance in 11 years with sales of 54,370 trucks last month.

Much of this strength comes from the new generation of the F-150. While many of the old model are still being sold off, Ford is rolling out the new version. Just five percent of the F-150's retail sales were the new truck in December, but it was up to 18 percent in January.

The increase comes as the first factory that makes the truck, Ford's Dearborn facility, is fully back online. The other F-150 factory, in Kansas City, is still completing its changeover to build the aluminum-bodied truck, and that's expected to be finished in the first quarter of this year. Sales of the truck will still be "tempered a bit" until the Kansas City plant ramps up, Ford sales analyst Erich Merkle said. Ford expects to have a full inventory of F-150s by mid-year.

To that end, the company announced plans on Wednesday to add 1,550 jobs to support the F-150, including 900 positions at the Kansas City factory. The remaining jobs will be spread out over sites in metro Detroit. The Dearborn and Kansas City factories collectively will be able to build more than 700,000 F-150s annually. The added headcount also means Ford has reached the maximum number of entry-level workers allowed under its pact with the United Auto Workers. About 300 to 500 employees at several plants in the Midwest will transition to a higher pay rate, and their wages will rise from $19.28 an hour to $28.50 an hour.

The F-Series was Ford's hottest seller in January, moving off lots in an average of 12 days. The high-end models, the King Ranch and the Platinum versions, are moving slightly quicker. The average transaction price is also up $2,100 for the F-150 compared to January 2014.