The engines deliver adequate acceleration, very linear. This is a heavy truck, however, weighing over two and half tons, empty, and we wouldn't call it quick. The transmission changes gears smoothly, although kickdowns for merging onto freeways or overtaking slower traffic were sometimes slow.
The 5.3-liter iron-block V8 is rated 320 horsepower and 340 pound-feet of torque. Its equipment code is LY5, which is important only to distinguish it from the LMG-code engine, which is a no-cost option with identical output ratings but is designed to offer flex-fuel capability to run gasoline or E85 ethanol.
The 5.3-liter V8 in the 4WD Avalanche has an aluminum block to save weight. Coded LC9, it is flex-fuel capable but rates a marginally less mighty 310 horsepower and 335 pound-feet of torque.
The L76 aluminum-block 6.0-liter V8 is optional for LT and LTZ models with 2WD or 4WD, rated 366 horsepower and 380 pound-feet of torque. It is not flex-fuel capable.
All three engines feature Active Fuel Management, which electronically shuts off four of the eight cylinders when they are not needed. A good idea in theory, but a truck as heavy as the Avalanche needs all eight cylinders nearly all of the time. In our test time with the Avalanche we covered around 300 miles, about evenly between interstate and local surface streets; and the telltale in the dash information display indicating cylinder de-activation appeared only on downhill grades or while coasting, most often to a stop. And this was without ever towing anything, or hauling anything heavier than a week's groceries. Running entirely on gasoline (we had no access to ethanol), our 4WD Avalanche averaged 14.4 mpg.
2008 EPA fuel economy estimates are 14/20 mpg City/Highway for either 5.3-liter engine with 2WD, 14/19 mpg with 4WD, 12/17 mpg for the 6.0-liter with 2WD or 4WD. Next Page