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2006 Chevy Silverado 2500 HD - Maximum MPG

The Search For Full-Size Fuel Economy

Photography by Courtesy of General Motors Corp.,

You don't have to drive a nerdy gasoline hybrid car to get good fuel mileage. You can maximize the miles per gallon achieved in a fullsize truck with a few flicks of a pen when you order a turbodiesel at the dealership. To test our theories, we ordered a two-wheel-drive Chevy Silverado 2500HD with the 6.6L Duramax engine and the Allison six-speed automatic transmission.

Transmission Truths
The Allison transmission has just as many speeds as the manual. Plus, it has higher overdrive gear ratios. The double-overdrive feature allows the Duramax to loaf along-even at highway speeds.

Model
ZF S6-650 (ML6)
Allison 1000 (MW7)

Type
6-speed manual
6-speed automatic

Gear Ratios
1st 5.79 3.10
2nd 3.31 1.81
3rd 2.10 1.41
4th 1.31 1.00
5th 1.00 0.71
6th 0.76 0.61
Reverse 5.23 4.49
Rear Axle 3.73 3.73
SOURCES
Chevrolet
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