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Discussion Starter · #1 ·
I picked up a Black Diamond Denali on the 4th and drove it 220 miles home. On the trip there my 17 Denali got 19mph on the way there driving about 80mph. On the way home i got 13. There wasn't any wind either.

I know it needs to break in a little but it's not going to come up 50%. I'm at nearly 700 miles now and the dash reads 14.1 avg.

Anyone else have an experience with the 10 speeds yet, and how they do on mileage? Any suggestions, dealer has already said come back after a few thousand miles.
 

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I got my 21 two weeks ago. Did a 350 mile trip with a lot of up and down hills. average was 16.8 running 78sh.
 

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I picked up a Black Diamond Denali on the 4th and drove it 220 miles home. On the trip there my 17 Denali got 19mph on the way there driving about 80mph. On the way home i got 13. There wasn't any wind either.

I know it needs to break in a little but it's not going to come up 50%. I'm at nearly 700 miles now and the dash reads 14.1 avg.

Anyone else have an experience with the 10 speeds yet, and how they do on mileage? Any suggestions, dealer has already said come back after a few thousand miles.
Regens will affect mileage
 

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Discussion Starter · #6 ·
Regens will affect mileage
i wish i could tell if it is or not. The dealership can't find **** unless there's a fault code to tell them what to do.
 

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i wish i could tell if it is or not. The dealership can't find **** unless there's a fault code to tell them what to do.
The dealership needs a code to appear so they can be paid by GM for any diagnostics/repairs. Otherwise, they don't care.
Having a Banks system w/ iDash or another type of Monitor can show you when your truck is in Regen.
 

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Discussion Starter · #8 ·
The dealership needs a code to appear so they can be paid by GM for any diagnostics/repairs. Otherwise, they don't care.
Having a Banks system w/ iDash or another type of Monitor can show you when your truck is in Regen.
They don't actually, lots of things break with out fault codes. They just don't know what to do without one.

I've looked at an insight but didn't want to spend $400 bucks to prove what it's doing. Does anyone know if any of the cheaper diagnostic scanners alert to a regen? If Banks and Edge can read it off the CANbus i would think the scanners might be able to.
 

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They don't actually, lots of things break with out fault codes. They just don't know what to do without one.

I've looked at an insight but didn't want to spend $400 bucks to prove what it's doing. Does anyone know if any of the cheaper diagnostic scanners alert to a regen? If Banks and Edge can read it off the CANbus i would think the scanners might be able to.
The Autel Maxicheck Pro is one. If you google you can find other sources
 

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My scantool.net OBDLink MX Bluetooth OBD2 adapter has a free phone app that can be downloaded for it. That app had free “extra PID” add-one, and the Duramax add-on has regen info in it. The adapter was $100 or less (they have several models).
 

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My 2021 isn't good, same as my deleted 2011 with lift & 35s. My buddies 2020 is much better.
 

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Discussion Starter · #12 ·
last tank hand calculated was 13.6 mpg. That tank had a 200mile run on it so not good. I did actually smell one of the first full regens. Time for another run at the dealership. i'm not waiting a few thousand miles. i love the truck but i'm certainly not keeping it if this is the expected performance. I hope they can get this thing figured out.
 

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I have kept cost & mpg records on my '04 LB7 and now my '20 L5P.
The LB7, a 2WD crew cab long bed, kept to 17-18 mpg around town, and 11-12 when freeway-towing a 20' travel trailer.

The '20 L5P, a 4WD crew cab long bed, has been showing 2-3 mpg lower mileage.
I'm not sure how much of that is due to the extra smog sh!t or the 4WD.
 

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Picked up my '21 Sierra 3500HD on the 20th and drove 600+ miles home. Driving through Idaho at 80+mph I was only getting 13.8mpg (~200 miles) by gauge, once I backed off to 65-70mph gauge showed I was getting 23.8mpg (~400miles). I was extremely disappointed to begin with, but please with the latest. I'll hand calculate from here on out to verify.
 

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2020 Silverado 3500HD Duramax/Allison, LT, Crew Cab, SRW, Std. Bed, Z71, 4WD,
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On my un modified trucks, I have found the DIC mileage to be very accurate. We just took a 240 mile trip and got 21 mpg in one direction and 19 coming back. 75-80 mph most of the way.
 

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Discussion Starter · #16 ·
I have kept cost & mpg records on my '04 LB7 and now my '20 L5P.
The LB7, a 2WD crew cab long bed, kept to 17-18 mpg around town, and 11-12 when freeway-towing a 20' travel trailer.

The '20 L5P, a 4WD crew cab long bed, has been showing 2-3 mpg lower mileage.
I'm not sure how much of that is due to the extra smog sh!t or the 4WD.
the 21's are about a 1k lbs heavier and have a 10 speed. i figured the 10 speed would help keep the rpm in the sweet spot to offset the extra weight... guess i was wrong.
 

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2021- 2500HD Silverado LTZ Z71 Diesel 4WD
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I’ve had my 2021 since November. I only have around 3500 miles on it and I only get around 12.5-13.5 MPG. My 2015 was much better. This one also seems to suck down DEF fluid as well.
 

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My 2020 Duramax gets 20.5 mpg cruising on the interstate at 60 mph and averages 15+ in mixed driving. It does use more def than prior years based on what I read on the forums, however, this is my first Duramax that uses it. I think the mileage is as good as my prior trucks. In the past I've owned a 2002 LB7 and a 2008 LMM. As far as I'm concerned, this truck is a hands down winner in every category.
 

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I picked up a Black Diamond Denali on the 4th and drove it 220 miles home. On the trip there my 17 Denali got 19mph on the way there driving about 80mph. On the way home i got 13. There wasn't any wind either.

I know it needs to break in a little but it's not going to come up 50%. I'm at nearly 700 miles now and the dash reads 14.1 avg.

Anyone else have an experience with the 10 speeds yet, and how they do on mileage? Any suggestions, dealer has already said come back after a few thousand miles.

I have a 2021 that I picked up March 1st, have about 675 miles on it with a mix of street and hwy. Haven't towed yet and I'm averaging only 9.8 MPG. Something has to be wrong!!
 
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