Surprisingly, fuel economy is 11% better in the new models. This is mostly due to a shift away from exhaust gas recirculation to the use of urea fluid to control exhaust emissions. Because of the use of urea fluid in this year's models to control exhaust emissions, the soot collection chamber needs 75% less frequent regeneration (or burning out). This saves fuel because the burning-out process is accomplished by injecting diesel fuel in the chamber to create the fire. (Regeneration needs to be done approximately every 700 miles.) The urea tank is accessed with a filler tube in the engine compartment; it needs to be refilled only at regular engine servicing intervals (approximately 5,000 miles). High-pressure Piezo fuel injectors are used for greater fuel economy, power and reduced emissions. Engine oil flow is increased for more oil pressure at idle and for faster delivery to the turbo. The engine is now B20 compatible.
The Allison transmission is beefed up with a stronger torque converter, a larger-diameter output shaft and more robust clutches. When the transmission is put into tow mode, the shift points occur at higher rpm, and when I took my foot off the accelerator, the engine began to immediately shift down. That feature along with the standard engine brake helps save brake pads and other brake wear. The Allison transmission also features a race-car-like tap up/tap down feature on the end of the transmission shift lever and a patented elevated idle mode cab warm-up feature. Performance of the Duramax/Allison combination is also improved over previous models with preliminary testing showing 0 to 60 mph in less than 9 sec. and quarter-mile times of less than 16 sec.
I took the truck over to my neighbor who has an identically equipped 2006 model. We ran them side by side and found the new truck is a little bit quieter at idle. When my neighbor drove the truck, he was most impressed by the better brakes! They are larger in diameter and width to deliver smoother, more immediate and confident feeling and performance. Wheel hubs and bearings are larger and complement the new brakes.