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If you're behind one, you can spot a diesel equipped HD from a distance.

Its tailpipe aperture is over 5-inches in diameter. You could bake a potato in this thing. The tip is actually welded on the exhaust about a foot from the back. It overlaps a smaller 3-inch tailpipe to create an opening that allows ambient air to quickly mix and cool off the hot engine exhaust from the emissions controls– so you don’t burn the paint off the car next to you at a grocery store when you park.

Can’t wait to see the massive chrome tips that start showing up in the aftermarket!

Other changes include new seven hole common rail piezo electric injectors that are safe for use with ULSD fuel and lower noise levels by precisely and variably injecting fuel multiple times during a single combustion stroke.

The GM trucks also use improved glow plugs in “park warm up mode” that heat up faster than Ford's PSD glow plugs and Dodge’s ambient air intake heater on the Cummins - saving up to seven seconds starting the engine over conventional glow plugs in extremely cold conditions.

All of this engine technology requires computing power. A new 32-bit controller manages the fuel injection, fan, and oxygen levels to precisely control engine temperatures, increase efficiency, and slightly raise fuel economy.

According to Gary Arvan, Chief Duramax Engineer, the LMM carries roughly two to three times the computing power over the original 2001 LB7 Duramax. And to meet even stricter 2010 emissions requirements, Arvan expects to see computing power jump another two-fold over the 2007 engine.

Even more amazing, while improving fuel economy and emissions, GM has raised the power ratings on the Duramax to a class leading 365 horsepower and 660 lb-feet of torque that can propel a regular cab HD from 0 to 60 mph in the low seven second range, according to Garvan.

The net result - as a passenger for this part of the ride, it was incredibly difficult to tell we were in a diesel given rapid acceleration runs from a dead stop and GM’s attention to interior noise reduction and very low levels of clatter at rest and under load.

The diesel's noise, vibration, and harshness levels are a major step up over the respectable NVH levels in the previous GMT800s.

The only thing the Duramax needs is a larger fuel tank. The 26-gallon tank, standard on short beds, provides a range of only about 400 miles. Long beds get a 34-gallon tank. Assistant GMT 900 vehicle chief Jully Burau responded to our questions about the relatively small range with the cryptic response, “to stay tuned.”

A large portion of this ride was on I15 at speeds up to near 80 mph. For such a massive vehicle there was very little wind noise to impede conversations between front and rear passengers, thanks to better aerodynamics and a stiffer frame that allows for closer positioning of the bed and cab to reduce the gap between these components.

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