In short, the Chevy Silverado's performance surprised everyone, given Ford's higher stated power figures for the 6.7-liter Power Stroke. Finishing two minutes ahead of the Super Duty over a 7.6-mile grade at more than 90 percent GCWR is nothing short of a dominant showing for Chevy. The exhaust brake performance is perhaps even more telling and welcome news for frequent heavy towers.

What accounts for the significant performance differences between the Chevy and the Ford in this comparison? We originally thought it might be a gap in the Power Stroke's high altitude engine calibrations, which optimize combustion performance based on driving conditions, but now we think its part of the nature of the 6.7's unique single sequential turbo.

Ford's turbo features a single turbine and two compressors placed back-to-back. It's possible that Ford's siamese compressor design is losing some efficiency the higher it climbs.

For braking, both trucks depend on variable geometry fins that surround the turbine. They clamp down to restrict exhaust flow and create back pressure in the engine to slow the truck down. The Duramax appears to be able to clamp down more strongly than the Power Stroke.

Interestingly, Honeywell subsidiary Garrett is the same turbo supplier for both diesel engines. 

Regardless of the cause of the performance gap between these two incredibly capable HD pickups, we reaffirm the results of our 2010 HD Shootout in the real world. There’s no question that GM's latest diesel pickups are the performance leaders in the class. Chevy doesn't just run deep. It runs high as well.

For more information and a second take on this test, be sure to check out Diesel Power.