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6 or 8 speed tranny

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redwngr Senior Enthusiast

redwngr

Posted
Posted

Mine has had several updates. the most recent was in late winter, and I think they`ve finally got it this time.

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arcasey Enthusiast

arcasey

Posted
Posted

I don't personally have an 8-speed but I have two friends that have the newer 2017 6.2L with 8-speeds and they are thrilled with them. I have a 2015 with the 5.3L and 6 speed and they both get considerably better mileage than I do with the 6.2L 8-speed combo. I can only assume the 5.3L with the 8-speed would do even better mileage wise.

n1ghtsh1ft Enthusiast

n1ghtsh1ft

Posted
Posted

2017 5.3L 8 speed here. No issues with my 8 speed. I think it is more designed for towing anyway, as I always seem to be in the power band when I need to accelerate.
The 2017 6.2L 8 speed is not as good in my opinion. I found it to be harsher in upshifting and a bit schizophrenic in stop and go traffic when I test drove it for a week.

It was a completely different experience from what I experience in my 5.3L 8 speed.

bosro Enthusiast

bosro

Posted
Posted

My 6.2L has had a jekyll n hyde attitude since day 1.

Clunky,harsh,pops....slow to engage when put In D when cold.

My truck was been in shop for almost a week for top end issues and I've been driving a rental with 5.3 and 6 speed.

The 8 speed is absolutely horrible compared to the 6....at least with my 15

It's pretty enlightening to drive them back to back.

Maybe Chev has refined the 8.....15s (like mine) were 1st year for the 8 speed....I would hope so

njk4o5 Enthusiast

njk4o5

Posted
Posted

6 speed or 8 speed you ask? honestly toss up a coin. because they both suck ass. the factory trans tuning in the both of them is horrible.

 

I have one of the higher mileage trucks on here at 96,400 miles and the dealer cant figure out whats wrong with my 6 speed. I have a feeling its the tuning but since GM hasn't come out with any new service bulletins for it I have to live with this shitty shifting truck

michigan2500hd Senior Enthusiast

michigan2500hd

Posted
Posted

Just got my 8 speed from the shop where they performed a update to the TCM. My paperwork says they also reprogrammed the ECT. Is this a typo? Wonder if they meant ECM? Here's they weird part.. They performed #16-na-364. When I look it up it references a Corvette with the 8 speed.

 

Sent from my E6810 using Tapatalk

mookdoc6 Senior Enthusiast

mookdoc6

Posted
Posted

With the power the 6.2 has I think the 6 speed is perfect. I've had both and I believe the 8 speed is a tick slower. It's not as predictable either. I had high hopes for my 8 speed but now the only high is being had by the morons that wrote the factory programming. I would trade for a 6 speed any day. I will say that when you really get on it from a stop it really works well. It's taking off slow and also stop and go traffic that it lacks in. Also the mysterious clunk that happens sometimes when you are almost to a stop.

 

It seems the eight is ok for towing and full throttle runs but the six is a better daily driver.

 

Sent from my E6810 using Tapatalk

 

 

That pretty much sums it up! If your towing frequently get the 8speed.....If your daily driving with traffic get the 6!

truckguy82 Senior Enthusiast

truckguy82

Posted
Posted

Blackbear tuned 6 speed with 6.2 owner here. Have had 2 sierra loaners with the 8 speed and rented a camaro SS for a week.

 

I'd go with the 8 speed if you have any plans whatsoever for mods. The factory tuning for the trucks is horrible.

 

All you need to do is take one drive in a camaro or vette to realize the 8l90 is one incredible trans. It can also handle a boatload of power stock. One of the best things about it is that it retains the power through the shift where as the 6speed will cut power during each shift. If you drive the camaro or vette, you will be amazed at how the 1-2 shift catapults you forward unlike any traditional auto trans you have likely ever driven. I really had no idea how much faster a car could be just because of the shifting until I drove a camaro ss with the 8l90.

mookdoc6 Senior Enthusiast

mookdoc6

Posted
Posted

Blackbear tuned 6 speed with 6.2 owner here. Have had 2 sierra loaners with the 8 speed and rented a camaro SS for a week.

 

I'd go with the 8 speed if you have any plans whatsoever for mods. The factory tuning for the trucks is horrible.

 

All you need to do is take one drive in a camaro or vette to realize the 8l90 is one incredible trans. It can also handle a boatload of power stock. One of the best things about it is that it retains the power through the shift where as the 6speed will cut power during each shift. If you drive the camaro or vette, you will be amazed at how the 1-2 shift catapults you forward unlike any traditional auto trans you have likely ever driven. I really had no idea how much faster a car could be just because of the shifting until I drove a camaro ss with the 8l90.

 

And there is the problem........The Tune will help on Silverado/Sierra problem is it's not a Vette/Camaro and the Torque/HP is undercut on these transmissions almost 200 per each? Hence, it shifts like assssssssss

 

No doubt it's a kick as TRANS! When it's in a Vette/Camaro! Other than that it's shit ass unless your inclined on mountain grade pulling just stomp it and the TRANNY IS ****ING MARVELOUS! In this city you will go home and slap your wife around because you have just been "Mind ****ed" by the 8speed in rush hour traffic!

truckguy82 Senior Enthusiast

truckguy82

Posted
Posted

 

And there is the problem........The Tune will help on Silverado/Sierra problem is it's not a Vette/Camaro and the Torque/HP is undercut on these transmissions almost 200 per each? Hence, it shifts like assssssssss

 

huh?

michigan2500hd Senior Enthusiast

michigan2500hd

Posted
Posted

I think the 8 speed in my Silverado COULD be awesome with the the tuning. As it is it feels less peppy in normal driving then the 2017 Sierra V6 M6 I just had as a loaner. That thing was actually impressive! Made me kinda rethink having to have the big bad 6.2. I was getting between 25 and 29 miles per gallon at 70 mph on a flat highway ( I-69 ) and the AFM would stay on fairly well taking the MPG's even higher. Kudos to GM on the 4.3.

 

Sent from my E6810 using Tapatalk

redwngr Senior Enthusiast

redwngr

Posted
Posted

Just got my 8 speed from the shop where they performed a update to the TCM. My paperwork says they also reprogrammed the ECT. Is this a typo? Wonder if they meant ECM? Here's they weird part.. They performed #16-na-364. When I look it up it references a Corvette with the 8 speed.

 

Sent from my E6810 using Tapatalk

The 8L90 (rpo M5U) is used in Sierra/Silverado, CTS-V, Camaro SS, Corvette, CorvetteZ51 (both behind LT1), corvette Z)^ (behind LT4), Escalade/EscaladeESV and the Yukon Denali/DenaliXL.

 

There is also an 8L90 Accum (rpo M5X) which apparently is a means it is for "automatic start/stop, with accumulator".

 

The 8L90 is produced in Toledo OH and Silao, Mexico.

 

http://gmpowertrain.com/assets/docs/2017-US-Product-Information-Guide.pdf

 

 

 

 

 

The Colorado/Canyon 8 speed is much lighter -- it is an 8L45

Bikemobile Enthusiast

Bikemobile

Posted
Posted

The 8 speed really shines on long climbing high speed grades. I can only compare my 8 speed to my old 4 speed but it climbs hills and mountains with ease. I just drove it 6 hours today out of town and I'm happier than ever with the truck.

 

It does surge sometimes into park and clunk oddly at low speeds. Maybe the next trans design will be figured out completely.

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