2014 - 2018 5.3 6 speed downshift jerks

Grumpy Bear · July 30, 2019

1 hour ago, mmmikkke said:

Is it the coffee, the radio, or the 6L80?

Yes!

Racindave · July 31, 2019

If I drive my truck like a mature person it’s super smooth taking off and stopping (especially if I run 89 octane). If I drive it like I stole it it gets all herky herky for a bit. Once I drive normal again it clears up. I’m just chalking it up to the transmission trying to save me gas and figuring out how I want it to drive. Honestly, I can live with it. Love everything else about it.

Bob2C · August 10, 2019

Installed Gibson exhaust and the harsh downshifting is gone.

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dieselfan1 · August 10, 2019

9 hours ago, Bob2C said:

Installed Gibson exhaust and the harsh downshifting is gone.

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I highly doubt the exhaust had anything to do with it.

Bob2C · August 10, 2019

I highly doubt the exhaust had anything to do with it.

Don’t know what else it can be. Been like that since new and now have 12k miles on it. The only thing different is the exhaust. Just weird

mmmikkke · August 11, 2019

17 hours ago, Bob2C said:

Don’t know what else it can be. Been like that since new and now have 12k miles on it. The only thing different is the exhaust. Just weird

It's conceivable that the TCM has a coding error that adapts to "idle" throttle position changes caused by having the a/c on (higher throttle position needed to idle at 600 rpm) or by having a less restrictive exhaust (lower throttle position needed to idle at 600 rpm). Perhaps there exists a coding error that mishandles the default idle throttle position and properly handles the other 2 throttle positions I described above.

I noticed on my truck that if I brake to a stop (using my left foot) while having the throttle only a tiny bit open, the 3-2 and 2-1 downshifts are much stiffer. So this could be a 3rd idle position.

Has any reader of this thread actually gotten revised/updated shift tables uploaded into their TCM by the dealer under warranty?

I challenge GM engineering to release a technical document describing the design objectives and features of this advanced transmission that learns how I drive. Does it compensate for how I drive? Does it shift earlier or later because it has learned I am a lead foot or slow poke? How long does the learned behavior persist? Or once it learns I am a lead foot, does it relearn only with a battery cable disconnect?

Or do we all have to get hptuners in order to fix these issues?

Jacoby · August 11, 2019

You hear that GM!!! You’ve been challenged.

Bob2C · August 11, 2019

The thing I did do but failed to mention was disconnect the battery while I installed the exhaust as stated in the installation procedure.

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dieselfan1 · August 11, 2019

39 minutes ago, Bob2C said:

The thing I did do but failed to mention was disconnect the battery while I installed the exhaust as stated in the installation procedure.

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That's odd they want you to disconnect the battery to put exhaust on it.

I don't remember that when I installed the Borla. Actually I didn't even read the directions.

Bob2C · August 11, 2019

That's odd they want you to disconnect the battery to put exhaust on it.
I don't remember that when I installed the Borla. Actually I didn't even read the directions.

I found it odd too but they said it had something to do with the computer learning the correct pressure so it didn’t throw a code. Maybe it was overkill.

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nluchau · September 4, 2019

So about 3500 miles ago GM put in a reman transmission as a customer satisfaction for me. I still feel the firm downshifts but not as bad. The one thing I notice now ever since the 2nd transmission is the upshifting seems a bit firm. If its cold and I increase throttle and hit 33mph it abruptly upshifts into 5th gear. 1st - 4th seem fine just when it hits 5 it feels like it drops into 5 vs a slow ease into 5. I'm not heavy on the throttle either. I talked to the service manager right when I first noticed it, a few days after getting it back from repair. He said to give it 3-4k miles and let him know if it still happens as the transmission has a learning curve. One thing I've also noticed is the trans fluid (when checked cold) is way up on the dip stick overfilled.

My question is what can the dealer do now with this abrupt upshift into 5. Would a tap reset, or any other reset possibly correct this?

Thanks for any info

mmmikkke · September 26, 2019

I'd have the dealer correct the fluid level free of charge since they're obligated to follow GM instructions when doing repairs. I can't imagine a TSB instructing the tech to overfill the transmission. If they claim the dipstick is wrong then have them get you the correct dipstick. SMH on your dealership.

mmmikkke · September 27, 2019

On 9/4/2019 at 11:15 AM, nluchau said:

So about 3500 miles ago GM put in a reman transmission as a customer satisfaction for me. I still feel the firm downshifts but not as bad. The one thing I notice now ever since the 2nd transmission is the upshifting seems a bit firm. If its cold and I increase throttle and hit 33mph it abruptly upshifts into 5th gear. 1st - 4th seem fine just when it hits 5 it feels like it drops into 5 vs a slow ease into 5... Thanks for any info

@nluchau, are you feeling the tcc (torque converter clutch) lockup? At light throttle, it can occur (is permitted by a data table in the TCM) any time after 2nd gear is engaged, so your 2-3 shift could happen simultaneous with the tcc lockup. At 1/8 throttle, with my truck, tcc lockup occurs after the 1-2 shift. At 1/4 throttle, with my truck, tcc lockup occurs after the 2-3 shift. This suggests the TCM has some leeway on its deciding when is a good time to lock. With my truck, the tcc lockup is much slower than the gear-to-gear shifts. The slow lockup deserves the "ease into gear" characterization, so I was wondering if you have the tcc lockup event properly categorized given that you didn't mention it.

With a cold transmission, below 32F, the TCM does not lock the tcc at any speed, until the transmission temperature gets above 32F. This can give people in colder climates additional diagnostic info...

Your thoughts?

nluchau · October 22, 2019

On 9/27/2019 at 10:27 AM, mmmikkke said:

@nluchau, are you feeling the tcc (torque converter clutch) lockup? At light throttle, it can occur (is permitted by a data table in the TCM) any time after 2nd gear is engaged, so your 2-3 shift could happen simultaneous with the tcc lockup. At 1/8 throttle, with my truck, tcc lockup occurs after the 1-2 shift. At 1/4 throttle, with my truck, tcc lockup occurs after the 2-3 shift. This suggests the TCM has some leeway on its deciding when is a good time to lock. With my truck, the tcc lockup is much slower than the gear-to-gear shifts. The slow lockup deserves the "ease into gear" characterization, so I was wondering if you have the tcc lockup event properly categorized given that you didn't mention it.

With a cold transmission, below 32F, the TCM does not lock the tcc at any speed, until the transmission temperature gets above 32F. This can give people in colder climates additional diagnostic info...

Your thoughts?

Mike - Sorry for not seeing this until now. I am certain I feel it locking up while accelerating. Does it feel like some torque is being added somewhat? I wish I could drive it once without it locking just to feel what the downshifts would be like. I'm pretty sure what I am feeling is the TCC unlocking and locking again during downshifts when coasting but its rather harsh and jerky when it occurs. In town driving sucks to say the least. Interstate travel is great of course since it stays in 6th. Wish I knew if this could be resolved or not. It appears not though...

mmmikkke · October 25, 2019

My truck's tcc lockup by itself is not harsh or jerky. For my 2016 Silverado 4.3L V6, harsh or jerky describes the 3-2 and 2-1 downshifts as I come to a very gradual stop and the tcc has not yet unlocked. At zero throttle, decelerating to a gradual stop, my truck's tcc seems programmed to unlock after the 2-1 downshift, just in time to NOT lug the engine before shedding those final 2 or 3 mph. In other words, under the described conditions, tcc unlocks at the "last minute" so that engine RPM stays above or at 600 (idle) as the truck slows to 3, 2, 1, and finally 0 mph. I'm considering buying an hp tuner at hptuners.com just so I can play with the tcc minimum speed (minimum unlock speed while decelerating). It seems if I could raise tcc min speed to maybe 10 mph. then the 3-2 and 2-1 downshifts would occur while the tcc is unlocked, and so the torque converter's fluid coupling would absorb the 3-2 and 2-1 downshift harshness and all would be good.