Just replaced my '06 LT with a '10 LTZ Z71 4x4, 5.3L. Love the truck, only 54k miles, picked it up in Dallas and drove it home to Greenville, SC.(955 fun miles). Gas mileage was a little disapointing. On our trip home we stayed right around 75-80 mph. The rear axle is the 3.08. The tires are 285's vs factory recommendation of 265. We averaged 14-15 mpg. Is this about right with all things considered? BTW, I love the 6 speed tranny.
Thanks in advance

 

my 04 silverado with the 5.3 gets only 10 mpg so i would say your doing better then mine is..

 

That is not that bad with a 4 X 4 doing 80.