One problem related to engine exhaust system has been reported for the 2008 Chevrolet Avalanche. The most recently reported issues are listed below.
The active fuel management (afm) system has failed causing the motor to lose combustion in one of the afm cylinders (cylinder 7 to be exact) due to the afm lifter failed and has jammed the exhaust valve open. Gm is aware of the issue and has had several complaints to fix. Everyone with the afm system from gm for around my model year have had similar problems or have completely lost the motor.