Poor MPG
 

I bought used, a 2011 silverado 2500 ex. cab 4x4, 6.0 liter, When I used 87 octane 10% ethanol I got 12.4 MPG at best. I am now using 91 octane, no ethanol and I am getting 12.9 MPG after three tank fulls. Can I expect better or is ther a problem. There was only 6000 miles when I bought it. And I now have 9000. 90% of my driving is interstate.

Octane should not affect fuel mileage. I'm betting your improved fuel mileage from 87 to 91 is due to NO ethanol.

As for mileage? Can't help you. I'm assuming your are talking city driving? And you might want to list the gear ratio so people can provide a better answer.

I have a Silverado 1500 with the 5.3L V8 and I have a hard time getting much over 15 mpg. If you want fuel economy, you bought the wrong vehicle. I love my Silverado, but it ain't a Prius by any stretch.

That is why I use my truck once or twice a week, but drive my old Nissan Sentra to and from work (28 miles each way) because it gets more than double the fuel mileage of my Silverado.

P.S. A guy at work has a 2005 Silverado 2500HD with the 6.0L V8. He gets 11 mpg in the city and about 13 on the highway. It is like pushing a brick through the wind.

stay away from ethanol blends and use 87 octane. The engine doesn't call for higher octane fuel so don't use it. There is more latent heat energy in 87 octane and if you don't have a high compression engine that requires higer grades your wasting your money. The only thing high octane fuel is better for in a low compression engine is for fuel storage but there is stabilizer for that anyway.

my 06 2500 4L80E 6L, 4.10 rear end, sierra got 19.6mpg 100% highway in the summertime. In the winter, stop and go 13mpg...yep

my fuel numbers are calculated using the imperial gallon.

In a 2500HD with a 6.0, 4.10s, and 4wd I'd say you're doin pretty good with 12.5 mpg in that setup

I notice about 20% better gas mileage with 100% gasoline.

We cannot buy 100 percent gasoline here - as the EPA mandates "reformulated gasoline" and E10 in our market. I guess we are stuck with it.
:o