The heavy-duty truck wars are always simmering, but new spy shots captured high in the Colorado mountains suggest General Motors is about to turn up the heat. Roman Mica from The Fast Lane Truck stumbled upon a convoy of camouflaged and heavily instrumented GM HD trucks testing on the infamous I-70 grade, sparking questions about a long-rumored new engine.

The Megamax Diesel Rumor and the Evidence

For over a year, TFLtruck has been sitting on a tip about a new, larger-displacement diesel from GM. “We received a report from an anonymous source with some credible information that General Motors is working on an 8.3-liter, so a really high-displacement turbo diesel V8 engine,” Andre Smirnov explained.

The rumored specs are massive: 600 horsepower and 1,200 lb-ft of torque. The new spy video is the first hard evidence that GM is deep into testing a new powertrain. The TFLtruck team spotted the convoy of Chevy and GMC trucks, all with Michigan manufacturer plates, as it towed heavy, three-axle gooseneck trailers. The team loaded the trailers with steel plates and other camouflaged trucks. Some rigs also featured extensive emissions-testing equipment, including strange, oversized exhaust tips that the team likely used for attaching sensors.

Reading the Tea Leaves

The presence of these prototypes running in public is a significant development. “Whenever you see the vehicles testing, it usually means they’re like 6 months away from being either unveiled or introduced officially,” Roman noted, based on his 15 years of experience. Andre predicts these will likely be 2027 models, unveiled sometime next year. The need for a new engine is clear, as GM is currently behind Ford when it comes to the never-ending torque wars.

More Than Just Power

While the horsepower numbers are exciting, a larger engine could offer other benefits. Andre mentioned that a bigger displacement engine might actually have an easier time with emissions, as it wouldn’t have to work as hard. “It’s easy for us to get excited about big horsepower numbers,” he said, “but I think more so it has better efficiency.”

The sighting has officially rekindled the excitement for the next chapter in the diesel truck wars. The possibility of a new 8.3-liter Megamax Diesel Silverado and Sierra is no longer just a rumor; it’s a very real development being put to the test on the toughest highways in America.