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Crappy trans shift profile - 2018 Sierra 6 Speed

CCGMC

By CCGMC
in Troubleshooting & Recalls

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CCGMC Enthusiast

CCGMC

Posted
Posted

I have a 2018 GMC Sierra with the 6 speed. I know this has been discussed on this forum but is there any remedy to the weak throttle tip in performance of this transmission? I have the 2018 model year so I assume I have the updated throttle peddle? I did the shim between the lower corner of the throttle plate and the firewall. It helped a little but in my opinion it’s still not right. I love everything about this truck but the transmission shifting. It just doesn’t seem right. Is there an update at the dealer I can do? 

1SLOW1500 Senior Enthusiast

1SLOW1500

Posted
Posted

The answer is.yes there is always something that can be done but not as simple as that.

It isn't just trans or throttle, or power.

When you say throttle tip in. I assume you mean you are rolling and get it pedal and it is slow or lags? It can be afm/DOD or fuel cut off a wot pass or down shifting. Or depending on demand and rpm torque management just blocking out the power.

CCGMC Enthusiast

CCGMC

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8 hours ago, 1SLOW1500 said:

The answer is.yes there is always something that can be done but not as simple as that.

It isn't just trans or throttle, or power.

When you say throttle tip in. I assume you mean you are rolling and get it pedal and it is slow or lags? It can be afm/DOD or fuel cut off a wot pass or down shifting. Or depending on demand and rpm torque management just blocking out the power.

Yes when rolling, slowing down and then getting on the pedal again it doesn't respond fast enough. I rented a 2018 Tahoe on a business trip with the 5.3 (6) speed and it was perfect. 

 

I was hoping the dealer has a fix for this as it's a well known condition. 

 

If it was related to AFM/DOD, fuel cut off or down shifting what would you suggest as next steps to improve it? 

1SLOW1500 Senior Enthusiast

1SLOW1500

Posted
Posted

There was a post not long ago that was a person same as you. Happy about truck but trans was ruining his drive quality. He had a tune done. With the trans and even the fuel tables with afm/DOD. And he raved about how much better it was and how he was amazed by the truck now.

Sent from my SM-N960U using Tapatalk

SierraHD17 Senior Enthusiast

SierraHD17

Posted
Posted

Gm is weird... it's like they honestly cannot tune anything remotely correct but then you get the odd good one.  I have never been a stock 6 speed fan and even my 2017s 6l90e was pretty blah.. has the usual 2nd 3rd flare when it's cold and whatnot.  Tuning helped but I have more work to do with it... Then out of left field I get this low mile bone stock 2013 6.2 NHT truck.

 

Honestly its 6l80e shifts perfect to the point of raising the wide open shift points higher is all I want to do.  Never hesitates, never gets lost or hangs up... never flares, nice positive shifts.. nothing.  Its bone stock... so who knows lol.  

flyingfool Senior Enthusiast

flyingfool

Posted
Posted

take a HP tuners class and do your research, then program your trucks trans, it will be 5X better then GM tune. GM tunes their ecus and trans-puters for different reasons, not for performance or long term reliability...! 

 

Sierra Dan Senior Enthusiast

Sierra Dan

Posted
Posted

AFM kicking in and out of V4-V8 most definitely affects transmission behavior.

Try Running it in M5 to see if it improves.

There is also a transmission "learn" mode that adjusts or sets the shift points to your driving style after around 1,000 miles or so.

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