The Ford Explorer is all-new for 2020, but while Ford Motor Company foresees smoother sailing ahead, the brand new design and its upmarket sibling, the Lincoln Aviator, have so far been little more than a headache for the automaker, not to mention a serious impediment to sales.

This month, Ford released it's US-market year-end sales report for 2019, revealing that Explorer sales were down 14.6 percent in the fourth quarter compared to the same period a year prior. That's hardly what any automaker hopes to see when it launches a completely redesigned product, but it actually represents a massive 52-percent increase over the previous quarter, in which US Explorer sales slid by 48 percent year-over-year.

Now, Ford's Chicago Assembly Plant - the automaker's oldest continually running production facility at nearly a century old - is turning out examples of the 2020 Ford Explorer and Lincoln Aviator at full pace. But the plant had to undergo a sweeping $1 billion, month-long transformation before it could start producing the new three-row utility vehicles - an uncharacteristically large plant revamp.

By the time it started producing again, the Explorer and Aviator were plagued by quality issues, and had "a slower [production] ramp up than we had hoped," Ford spokesperson Kelli Felker told the Chicago Tribune. She confirmed that thousands of early 2020 Explorers had to be shipped to Flat Rock, Michigan for quality control after rolling off the line.

Asked about the quality issues last month, Ford President of Automotive Joe Hinrichs freely admitted that Ford "took on too much" with the simultaneous launches of the Ford Explorer and Lincoln Aviator. Early examples of each model were reportedly stricken with issues ranging from missing components and transmission bugs that created a vehicle rollaway risk, to air-conditioning systems that only blew hot air.

"It was not like every single vehicle had to necessarily have fixes," Felker said. "But every single vehicle had to be inspected to determine if it needed fixes."

Despite the limited availability of the Ford Explorer and Lincoln Aviator, Ford Motor Company as a whole saw its US sales decline just 3 percent in 2019, reflecting industry-wide trends.