Oftentimes, Fiat Chrysler Automobiles (NYSE:FCAU) is a distant third when considering Detroit's big three automakers, with Ford and General Motors taking much of the spotlight. Despite being an afterthought, though, Fiat Chrysler Automobiles' sales are surging in 2014 because of the strong sales from its popular Jeep and Ram Truck brands.

However, even with sales surging this year, Chrysler is continuing to lag far behind its competitors in two critical categories, which will continue to limit the automaker's successful sales push. Here's a look at the two factors, and what it means for the newly debuted stock.

It's all about the fuel economy
One large selling point for automakers and dealerships in recent years has been improved fuel economy with newer models. Despite gas price volatility, better gas mileage will continue to be a strong factor for car buyers, and automakers lagging behind will feel some impact.

Which automaker ranked dead last in the U.S. industry in fuel economy?

If you guessed FCA, you'd be correct. FCA ranked dead last compared to all brands of automakers in the U.S. market, according to the EPA's annual Fuel Economy Trends issued mid-October for the full year 2013. FCA checked in with an adjusted fuel economy, across its lineup of vehicles, averaging 20.9 mpg. The industrywide average was 24.1 mpg.

FCA's full-size truck sales don't help mpg figures. Source: Fiat Chrysler Automobiles.

Now, we also have to consider that one reason FCA trails the entire industry is because of its dependence on sales of trucks and SUVs, which obviously get poor fuel economy compared to Japanese automakers' passenger cars.

However, even compared to its Detroit rivals, Ford and GM, FCA still checks in as a distant third. Ford and GM have 22.2 mpg and 22 mpg averages, respectively.

While ranking dead last in the industry in terms of fuel economy is no selling point, don't look for this to negatively impact sales, as consumers wanting FCA's popular SUV and truck products will continue to buy them. The next factor that Chrysler largely trails its competitors in, though, may be a different story.

Or is it all about reliability?
When looking at Consumer Reports' recent reliability report, FCA loyalists and investors both cringe. First, it should be noted that this report doesn't grade automakers as an entire unit; rather, it grades individual brands. Unfortunately, that only makes the pain much more obvious for FCA.

Let's start from the top, with the winners from the reliability report. Not surprisingly, Japanese automakers owned the top four spots, with Lexus taking the No. 1 honors, followed by Toyota, Mazda, and Honda.

Looking at the bottom, Dodge took 25th, followed by Ram, Jeep, and then Fiat in last place. Sadly, all four of those brands are under the FCA umbrella. Ford, which has been plagued by a buggy infotainment system rather than large reliability problems, ranked 23rd, while its luxury Lincoln brand jumped more spots than any other auto brand, to rank 15th.

Let's also take a look at how the automakers did overall when grouping the brands together. GM ranked as the most reliable of American automakers, which might come as a shock after the troubled automaker has recalled more than 26 million vehicles in the U.S. this year. Despite being the most reliable major American automaker, GM still trailed the industry average by 16% -- Ford lagged the industry average by 25%, and Chrysler checked in behind the industry by a whopping 69%.

Bottom line
Fiat Chrysler Automobiles recently debuted on the NYSE, offering U.S. investors a way to tap into a surging automaker that relies on profitable SUV and full-size truck sales. However, investors would be wise to temper expectations as two factors that have led Toyota to dominate the globe -- great fuel economy and reliability -- continue to elude FCA.

For FCA to be a viable long-term investment, the company must prove it can improve fuel economy and reliability, and design passenger cars that people want to buy -- in addition to keeping sales of its SUV and trucks surging. Investing in FCA right now is definitely risky, but it's an investment that could pay off if the company can indeed improve these two factors across the next decade.