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All this 17-20 mpg wether its highway or city is all foreign to me . I have an 11 with 10000 miles and have always averaged 13.5 mpg with combo of city and highway driving .

I took her n earlier this week for the flash for the po299 dtc that i only got once and recieved doc2558332 bulletin reflash . I have also noticed once maybe twice the steam from under the hood passenger side but at the time didnt know ....thought maybe it was steam from it being so cold .

I guess im just wondering how this is so diverse ....from 10mpg to 22mpg .
 

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Priceless - There is a HVAC drain hose on the right side of the firewall on the engine side - down at the bottom. If the hose is not turned towards the 8-9 o'clock position it can leak onto the exhaust and lead to steam and a faint diesel smell. Often can be noticed at slow speeds when making left turns. I had this on a truck I was driving and made it go away easily by turning the hose. Hope that might help.
 

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Anyone claiming 17-20 MPG in the city needs their head examined or needs a clear definition of city driving. The LML definitely gets better mileage than the LMM stock vs. stock, but it's still a heavy truck with a 400+ CID engine. I average 14.5 MPG pretty consistent with a mix of city and highway driving, and if there isn't a head wind (good luck in West Texas) I can manage 18-19 MPG, depending on how heavy my right foot is. FYI, I'm about to roll over 18,000 miles on my truck. I am very pleased with the mileage for a 100% stock truck that gained another 700 lb. of weight over the previous truck. It seems to average what my '08 LMM did with a tuner and exhaust. I think that's doing well considering the truck will regen once per tank of fuel!

Trevor
 
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I have 8112 miles on my 2011 LML. I have purchased 665.1 gallons of fuel since I picked it up. That's an average of 12.2 mpg. This is all hand calculated. I have kept a log since purchase. These numbers are true and accurate for my truck. I would have to say it is a 50/50 mix of city and highway.
 

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I have 8112 miles on my 2011 LML. I have purchased 665.1 gallons of fuel since I picked it up. That's an average of 12.2 mpg. This is all hand calculated. I have kept a log since purchase. These numbers are true and accurate for my truck. I would have to say it is a 50/50 mix of city and highway.
My info on my OnStar app shows a lifetime MPG of 12, but half of my miles have been with a 30' or 48' trailer behind the truck.
 

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my info on my OnStar app shows 14mpg lifetime and 10854 miles and i live in southern California so even some of my highway mile are like city miles and i tow 36foot bumper pull toy hauler @13klbs every other weekend. I have had my truck seance November 5th 2010
 

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I have come to the realization that these trucks like to run....fast. In town, I'm looking at 14-15mpg. At hwy speeds of 70-75, its about 16-17mpg. For some reason, the 80-85mph get me the best mpgs......like 20mpg+. I picked up this truck on Oct 1 and just rolled 14,000 miles this morning.
 
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My truck was averaging around 20 mpg running 78 down the interstate, but at 65 I'm getting 16-18 with it just rolling over 3000 mi before I put it in storage. I'm in Idaho so those numbers depend on the wind. Wither way it is better than my LMM with Ram Air and exhaust.

I agree that these trucks wanna run, i have to use cruise on base and in town.
 

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interesting

My truck was averaging around 20 mpg running 78 down the interstate, but at 65 I'm getting 16-18 with it just rolling over 3000 mi before I put it in storage. I'm in Idaho so those numbers depend on the wind. Wither way it is better than my LMM with Ram Air and exhaust.

I agree that these trucks wanna run, i have to use cruise on base and in town.
I have not hit 80 MPH yet, but I have noticed that the traditional 55 MPH that usually gets the best mileage does not with my Denali LML. Maybe the MPG sweet spot on these new LML's is closer to 80 MPH, very interesting.
 

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i to have seen best mpg at around 80mph. between 75 and 80 is where i run when i can and that seams to be best
 

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:D:D That's a sweet spot i can live with! :D:D
 

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I have come to the realization that these trucks like to run....fast. In town, I'm looking at 14-15mpg. At hwy speeds of 70-75, its about 16-17mpg. For some reason, the 80-85mph get me the best mpgs......like 20mpg+. I picked up this truck on Oct 1 and just rolled 14,000 miles this morning.

What kind of RPM is it running at 70mph? And at 80mph?

Are you running the stock tire size too?
 

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I can get up to about 17 on the freeway until the regen kicks in, then it's usually when I need to get off the freeway. After that driving in the city in regen mode my mileage will drop down to about 13. After the regen is done my mileage will creep back up to around 14.
 

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What kind of RPM is it running at 70mph? And at 80mph?

Are you running the stock tire size too?

My dually is completely stock.

@60mph - 1500rpm
@70mph - 1700rpm
@80mph - 2000rpm
 

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my info on my OnStar app shows 14mpg lifetime and 10854 miles and i live in southern California so even some of my highway mile are like city miles and i tow 36foot bumper pull toy hauler @13klbs every other weekend. I have had my truck seance November 5th 2010

great...i hope GM doesnt have access to that info. They could say your mileage went up, you are using tuner, and now your warranty is void
 

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They do.

great...i hope GM doesnt have access to that info. They could say your mileage went up, you are using tuner, and now your warranty is void
Of course they do, but they have it anyway with the trucks ECM or any other control module, most manufacturers have had the information for years. The insurance companies have been using the information for dtermining fault in accidents by reviewing speed, braking and now even directional elements like pitch, yaw, and roll, not to mention other inputs. And the manufacturer can use the info to void warranties. Big Brother at it's best.
 

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great...i hope GM doesnt have access to that info. They could say your mileage went up, you are using tuner, and now your warranty is void
but i am completely stock other than a dpf back exhaust. so there is no way they can even say i have a tuner. i just go on long drives like 1000mile round trips to northern California.
 

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I have come to the realization that these trucks like to run....fast. In town, I'm looking at 14-15mpg. At hwy speeds of 70-75, its about 16-17mpg. For some reason, the 80-85mph get me the best mpgs......like 20mpg+. I picked up this truck on Oct 1 and just rolled 14,000 miles this morning.
I'll probably get flamed for this but what the heck. With the old LBZ pulling our fifth wheel there's a streach of interstate 25 north of Raton, NM that is a great highway and you can run around 80. The truck just runs great pulling at that speed and the mileage by display is better than when running 65. Doesn't make sense especially with the wind resistence but it has always proven to be correct going and coming. I expect the LML to be no different.
 

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Anyone claiming 17-20 MPG in the city needs their head examined or needs a clear definition of city driving. The LML definitely gets better mileage than the LMM stock vs. stock, but it's still a heavy truck with a 400+ CID engine. I average 14.5 MPG pretty consistent with a mix of city and highway driving, and if there isn't a head wind (good luck in West Texas) I can manage 18-19 MPG, depending on how heavy my right foot is. FYI, I'm about to roll over 18,000 miles on my truck. I am very pleased with the mileage for a 100% stock truck that gained another 700 lb. of weight over the previous truck. It seems to average what my '08 LMM did with a tuner and exhaust. I think that's doing well considering the truck will regen once per tank of fuel!

Trevor
With almost 17k on here I get 16 city and 19.5 hiway. Mixed around 17.5. I do know what city driving is.

Now with zero temps its another story. 13-14 city but can still pull 18.5 hiway. Mixed about 16.

This is hand calculated too, no stupid DIC. Never have one that was right.

Greg
 
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