The 2014 5.3L V8 is rated up to 23 mpg, the only EPA rating that has been released by GM. The 5.3L is SAE rated 355 hp and 383 lb-ft torque, and rated to tow up to 11,500 pounds in a half-ton.
The 2014 6.2L V8 numbers were released today, as Chip pointed out, estimated at 420 hp and 450 lb-ft...