Investors and analysts widely recognized that the U.S. automotive industry was going to have a tough May, at least as far as year-over-year sales comparisons were concerned. That's because last month had two fewer selling days and one less weekend on the calendar, giving last year's May a significant advantage for selling vehicles. Because of that, the industry logged its steepest monthly sales drop in six years, and some of the declines, such as Toyota's and General Motors' (NYSE:GM) respective 9.6% and 18% drop, were huge.

Still, when considering the fewer selling days and one less weekend, the industry's seasonally adjusted annual rate was still a very healthy 17.46 million during May. Let's dig into the highlights from Ford Motor Company (NYSE:F), Fiat Chrysler Automobiles (NYSE:FCAU), and General Motors.

Ford: 235,997 units sold -- 5.9% YOY decline

Ford's 2017 Escape. Image source: Ford Motor Company.

The disatvantages of a May with two fewer selling days and one less weekend, at a time when sales of passenger cars are slowing in favor of SUVs, made for a brutal-looking car segment. Consider that Ford's best year-over-year sales increase, ever, within its passenger car segment was the Fusion -- and it declined 21.5% in May. Thes two worst year-over-year changes were the Taurus and Fiesta, with respective declines of 37.4% and 34.8%, and Ford's entire car segment was down nearly 26%.

On the flip side, though, Ford's SUVs sold well considering last month's unfavorable calendar situation. Ford's Escape posted a 6% gain for nearly 31,000 units sold last month, and its Ford Brand SUVs have sold more than 325,000 units through May. That's a 9% gain and the best-ever start for the automaker's namesake-branded SUVs. Strong SUV sales and the F-Series posting a 9% sales gain to more than 67,000 units last month helped drive the automaker's average transaction prices nearly $1,500 higher per vehicle -- roughly 50% higher than the industry, according to Ford.

Another bright story for Ford investors is the continued Lincoln turnaround story. Lincoln sales moved 7% higher in May, which marks six straight months of gains. That figure was helped by the all-new Lincoln MKX, which posted an 88% sales gain to 2,794 units. In fact, it was Lincoln's best May for SUV sales since 2003.

General Motors: 240,450 units -- 18% YOY decline

2016 Chevrolet Cruze. Image source: General Motors.

GM posted a steep 18% decline in total sales -- which was much worse than the competition -- for a couple of reasons. In addition to the calendar issues the rest of the industry is facing for May's comparison, GM has been substantially reducing its rental-fleet sales and had to deal with production hiccups at Fairfax, Lordstown, and Spring Hill because of the Japanese earthquakes.

Because of GM's reduction in rental-fleet sales, the company has focused on reporting its sales to retail customers. Retail sales checked in at 190,613 units last month -- still down 13% from last May. GM's fleet sales were quite a bit lower than Ford's: The category generated only about 21% of GM's May total, while fleet sales accounted for 32% of the total for Ford.

"We continue to execute our retail-focused sales strategy and maintain disciplined inventories and incentive spending with great products," said Kurt McNeil, U.S. vice president of sales operations, in a press release. "Our incentives continue to be well below our domestic and many Asian competitors."

That discipline has played out well for GM's highly profitable full-size trucks, the Chevrolet Silverado and Sierra. The sister trucks posted their highest average transaction prices on record during May, according to GM. Also, GM's incentive spending as a percentage of its average transaction prices was 9.8% during May, much below its domestic competitors' and below many of its Asian competitors' -- the industry average was 10.6%.

Fiat Chrysler Automobiles: 204,452 units -- 1% YOY increase

2015 Jeep Renegade. Image source: Fiat Chrysler Automobiles.

Of the six major automakers, FCA was the only one to post a year-over-year sales gain during May, while GM, Toyota, Ford, Honda, and Nissan all declined. That tiny gain, though, managed to extend the company's streak of year-over-year monthly sales gains to 74. The small gain was largely thanks to its Jeep brand, which continues to sell very well.

Of the five FCA vehicles that set sales records for May, three belonged to the Jeep brand. The Renegade and the Patriot posted their best monthly sales ever, and the Compass turned in its best May sales ever. That helped drive the Jeep brand to its best monthly sales ever, seeing a 14% sales increase in May compared to the prior year.

The Ram truck brand has also been a driving force for FCA this year, and that continued in May. Last month Ram truck brand sales were up only slightly -- only 15 more units sold compared to last May -- but that was good enough to squeak by for its best May sales since 2005.

On the downside, FCA's Chrysler brand continues to struggle in the U.S. with sales down 19% in May, and down the same 19% for the full year through May. Its Dodge brand posted a 5% decline in May, but has managed to increase sales by 6% for the full year.

Ultimately, while May appears to have hit automakers hard, the industry's seasonally adjusted annual rate remains a very healthy 17.46 million. As long as sales of full-size trucks and SUVs remain red hot, incentives remain in check, and transaction prices climb higher, expect these three automakers to continue posting strong bottom-line profits each quarter this year.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.