I have an 09 Silverado crew cab 1500 z71 and I got about 16-17 avg. before my cold air intake. about 17 miles of interstate/hwy and 2 or 3 miles in 5 oclock traffic after work each work day.

 

amurphy021 Welcome to the forum

 

I just want to make a note for the record here My old extended cab Z71 4 X4 with it's 4.8 4 speed trans and 3.73 gear can run circles around my new to me 2011 5.3 6 speed trans with AFM and 3.42 gear. Like 3-4 MPG if not more at times. I was in the 20 MPG range all the time when not towing or loaded with the 2000. Now in the 17 or less MPG range with 30 additional cubic inches and all the bells and whistles. Very dissapioned with GM right at the moment. I may try to put a 3.73 gear in it when the funds permit. you can feel the 2011 drag braking when you let off the gas. So it's a lot to overcome when moving forward.

 

Just traded my 2010 Z71 LTZ Double cab, 5.3, 3.42, 18's in. Put 184,000 on it. Put 10,225 gallons of gas in it for an overall average of 18. When I pulled my trailer, it dropped to 7-10.5 MPG using 89 octane. Never got better than 19.5 under any conditions.

New 2015 CrewCab, LTZ Z71, 5.3, 3.42, 20's is averaging 20.1 so far with 6,250 miles on it. (calculated, not from the instrument panel)

 

my 2008 ltz gets 16 with afm turned off

 

I have always believed that the mileage numbers on the window stickers are inflated. In real life, none of my vehicles has ever got mileage as high as the sticker.

I would like to second the posts that say that there is no advantage to using higher octane gasoline than what is recommended in the owners' manual. Lots of sources have confirmed that higher octane gas does not increase mileage.

Lastly, these are trucks. They have the aerodynamics of a horizontal outhouse. They weigh a lot, and high fuel consumption is just part of the territory. I have not checked the mileage on mine yet (98 with 5.7 litre), but am not expecting much in this regard.

My 1971 GMC 1500 with a 350 and Quadrajet carb managed to get around 12 in town if I was lucky, and maybe 16 on the highway. So, despite all the improvements in technology over the years, mileage in pickups has not really improved a heckuva lot.