As consumers of cars and trucks, we've gotten used to seeing fuel economy numbers go up every year like clockwork, even as we expect more power and torque and capability from our vehicles. It's because of this that Chevy and GMC's light truck numbers going down for 2019 seemed like such a head-scratcher.

The GM trucks' drop combined fuel economy was pointed out by everyone's favorite automotive sleuth and master of vehicular esoterica Bozi Tatarevic on Twitter on Friday, and like many of his discoveries, we found we had to dig deeper and find out why. After all, Chevy did make a big deal out of the increased aerodynamic efficiency and reduced weight when it debuted the Silverado 1500 back in January, so what gives?

Keep in mind, the trucks we're talking about all have the 4.3-liter V6 and 5.3-liter V8 engines and six-speed automatic transmissions. There were no advertised changes in the engines or transmissions between the two model years, though, as Bozi points out in his Twitter thread, the gear ratio at the rear end for the 5.3-liter model did change. That should account for some of the discrepancy but what caused the rest of the change? According to GM, it's size and capability.

"We increased towing capacity, payload, and it's a much larger bed and a much larger cab," said Monte Doran, a spokesperson for GM, in a statement to Automotive News.

So, the 2019 truck, despite being several hundred pounds lighter than the 2018 model that it replaces, is physically larger. It also has a front end with the aerodynamic efficiency of an overfed pug, and that's likely where the bulk of the drag is coming from. That also makes us extremely curious how the even more upright, square and generally brick-like front end of the new Silverado HD will fare in government fuel economy tests.

With all the emphasis on lowering corporate average fuel economy ratings, it will be interesting to see how General Motors compensates for this drop and if it will tweak the trucks further for the 2020 model year to eke back some of that efficiency.