[BoiseRob]

It's the same trans as far as function and size but they are not interchangeable for brand identity and they do have different torque converters

Where's the cut-away pic of the GM 10 speed? Why does the Ford specs identify 18qt capacity but the GM version has the fluid capacity missing? Why is the weight of the GM missing?

Hopefully Mike L. will chime in with his expertise since I am paraphrasing his post from another forum...

 

[Jamiecoyle21]

If the took it up to 60 on the flat with the computer hooked up, it would seem likely that they checked what gear it got into.

Curious to hear more about this. Certainly sounds like it has an issue.

Yes it ran through all gears

 

[Jamiecoyle21]

Well guys. UPDATE. After 25 minute drive with Diesel tech and computer hooked up, no changes 13.2 mpg flat highway, tech was like that ain't right. Unhooked computer and left dealership. Drove 17 miles on relatively flat highway at 60 mpg, note 8 miles was the same we tested on. Bingo 27.2 mpg. And 19.6 mpg around town. Tech can't believe it. Same thing today. WTF.

 

[laknox]

Severe gas mileage issues. My 2019 with same 6.6L engine got 26mpg hwy 19 mpg cityand had 8 speed trans. Brand new 2021 2500hd diesel gets 16mpg hwy and 13 city with the 10 speed Alision. Seems like it doesn't go over 6th gear. I tested with rpm gauge at 60 mph on flat highway in Drive. Dropped shifter to manual and it's in 6th gear not 9 or ten. Also downshifts at speed when foot comes off throttle. Dealership today put on computer 45 minutes, No Codes. Hopefully someone can respond with help. 2800 miles and only trailered a bass boat once at 14 mph hwy. Ugh

2800 miles? Damn thing is brand new! My venerable '02 had about 9k miles on it when I picked it up in '04 and it was at around 30k miles that I noticed a jump in mileage of about 1-1.5 mpg, average. Let it get broken in before you start complaining.

Lyle

 

[viper8315]

Weird, hopefully your issue is solved.

 

[durabroke]

Severe gas mileage issues. My 2019 with same 6.6L engine got 26mpg hwy 19 mpg cityand had 8 speed trans. Brand new 2021 2500hd diesel gets 16mpg hwy and 13 city with the 10 speed Alision. Seems like it doesn't go over 6th gear. I tested with rpm gauge at 60 mph on flat highway in Drive. Dropped shifter to manual and it's in 6th gear not 9 or ten. Also downshifts at speed when foot comes off throttle. Dealership today put on computer 45 minutes, No Codes. Hopefully someone can respond with help. 2800 miles and only trailered a bass boat once at 14 mph hwy. Ugh

I don’t know what world u live in but tell me where ur 2019 is. I want to buy it. I’d bet my truck it doesn’t get 26 mpg. You need a new calculator not a tranny

 

[NolaWelder]

I don’t know what world u live in but tell me where ur 2019 is. I want to buy it. I’d bet my truck it doesn’t get 26 mpg. You need a new calculator not a tranny

And 27 mpg on the ‘21?? We are talking about a Diesel right?

 

[ibulleti]

According to the DIC I got 27 mpg on a short trip Monday. I have only hand calculated my mileage once and it was 1.5 mpg higher than the DIC. My 2021 3500 only has 3500 miles on it and I usually get 22-23 on the highway and 14-15 around town. I have noticed the DEF recharge absolutely destroys mileage. I am taking the same short trip tomorrow and I will check the mileage again.

 

[NolaWelder]

According to the DIC I got 27 mpg on a short trip Monday. I have only hand calculated my mileage once and it was 1.5 mpg higher than the DIC. My 2021 3500 only has 3500 miles on it and I usually get 22-23 on the highway and 14-15 around town. I have noticed the DEF recharge absolutely destroys mileage. I am taking the same short trip tomorrow and I will check the mileage again.

Please do. The only time I had driven mine I got 14 mpg highway. Maybe it was getting poor milage because of the faulty def heater? Now that it’s replaced maybe I will get better. Or maybe it needs to break in. 600 miles only. First time buying a new vehicle so I’m definitely going through a learning curve

 

[sambor]

According to the DIC I got 27 mpg on a short trip Monday. I have only hand calculated my mileage once and it was 1.5 mpg higher than the DIC. My 2021 3500 only has 3500 miles on it and I usually get 22-23 on the highway and 14-15 around town. I have noticed the DEF recharge absolutely destroys mileage. I am taking the same short trip tomorrow and I will check the mileage again.

For the millionth time on this forum- DEF has nothing to do with mileage or regens. It is being used pretty much all the time to control oxides in the exhaust. More fuel you use higher the DEF usage.

 

[duecedriver]

For the millionth time on this forum- DEF has nothing to do with mileage or regens. It is being used pretty much all the time to control oxides in the exhaust. More fuel you use higher the DEF usage.

yes.. amen..

and to add.. not just the fuel.. but any time the engine sees an increase in NOx.. (generated by high heat combustion ) it will increase dosing rate (more DEF) AND increase EGR duty cycle (to bring down temps) and EGR introduces unburnable air thus REDUCING POWER lowering MPG efficiency ..

thus.. whenever you make more power, you will use more DEF and more DIESEL
if any sensors are not working properly my may use MORE DEF and get reduced MPG
if you are quick on the throttle (would roll coal without a DPF) you will use more DEF and MORE DIESEL
etc ...

 

[ibulleti]

Just finished one way on my trip. About 35 miles and “only” 22.4 mpg.

 

[duecedriver]

Just finished one way on my trip. About 35 miles and “only” 22.4 mpg. View attachment 1084226 View attachment 1084228

Gotta love that 10 speed for mpg. Let’s hope it lives up to the Allison branding!

 

[redwngr]

Well guys. UPDATE. After 25 minute drive with Diesel tech and computer hooked up, no changes 13.2 mpg flat highway, tech was like that ain't right. Unhooked computer and left dealership. Drove 17 miles on relatively flat highway at 60 mpg, note 8 miles was the same we tested on. Bingo 27.2 mpg. And 19.6 mpg around town. Tech can't believe it. Same thing today. WTF.

Did the tech verify that it was not in regen when it was getting about 13mpg?

 

[LMLLover]

Bingo 27.2 mpg. And 19.6 mpg around town.

 

[ibulleti]

Traffic and rain on the way home.

 

[ibulleti]

For the millionth time on this forum- DEF has nothing to do with mileage or regens. It is being used pretty much all the time to control oxides in the exhaust. More fuel you use higher the DEF usage.

Since I have only had this truck 42 days I may have missed the other million posts. I will start searching for them immediately.

 

[sambor]

Take your time , lots of info to digest.
LOL

 

[Midwest Cruiser]

An edge cts or banks idash will tell you what gear you are in, and if your tq converter is locked or not.

It's one of the many features I love about my iDash.

 

[Midwest Cruiser]

yes.. amen..

and to add.. not just the fuel.. but any time the engine sees an increase in NOx.. (generated by high heat combustion ) it will increase dosing rate (more DEF) AND increase EGR duty cycle (to bring down temps) and EGR introduces unburnable air thus REDUCING POWER lowering MPG efficiency ..

thus.. whenever you make more power, you will use more DEF and more DIESEL
if any sensors are not working properly my may use MORE DEF and get reduced MPG
if you are quick on the throttle (would roll coal without a DPF) you will use more DEF and MORE DIESEL
etc ...

Sounds like a vicious cycle, no thanks to all the emissions crap.