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Discussion Starter · #1 ·
I've been looking over the internet for a month now with no luck so I've decided to post here and ask about my trans issue. 2012 Z71, 5.3l, 6l80e with 138k mi.

When applying medium acceleration - enough to make the truck downshift to pick up speed - the transmission will pause/stall for 1-3 seconds then jolt/jerk into gear. If I hammer on it (pedal to the medal?) it functions as it should. I don't think it's slipping out of gear as the motor isn't revving up like it's out of gear during this hesitation. It's more like the motor and trans are being put on pause by a computer before the jerky downshift. After the pause and jerky downshift the truck drives and picks up speed as it should.

This usually happens at highway speeds when I hit the gas to pass someone, but will occasionally do it on city streets when accelerating/downshifting. This is the only issue I have - everything else works and shifts as it should. I've recently taken it to a Chevy dealership and they installed an update on the transmissions computer (TCU) and said they found no other issues. This seemed to correct the jerking downshift for 2 days, but it returned after that. I've also replaced 12 qts of the trans fluid, but didn't help (or hurt) the issue.

Any suggestions?
 

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Welcome to the site.
I wonder if your in V4 mode and the shifting to V8 before acceleration is the delay your having. Try driving around in M5 drive mode to see if you still experience it. This will not allow V4 to function, hopefully eliminating the delay your having.
 

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2010 GMC SIerra All Terrain C.C. 4x4 5.3
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1-3 seconds sound way too long. Are you sure it is that...or is it just excessive in your mind? I had a few quirks that the trans had from the factory in my 2010...getting a custom tune helped get rid of most of the quirks immensely.
 

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Discussion Starter · #4 ·
Rambodog - I've watched the V8-V4 display screen and it's showing V8 when this happens - so as far as that screen is showing (being in V8) the transfer to V4 to V8 isn't the cause because it's already in V8. It could always be faulty so I will try driving in M5 and see what it does. If the issue is no longer present in M5, will one of those Range AFM boxes that you plug into your OBDII port fix it? The Range is supposed to delete the V4 (or Active Fuel Management) as long as it's plugged in.

Nealinator - It might not be quite 3 seconds, but definitely 2. A custom tune was something I've thought about but know absolutely nothing about them or which to go with. Also, I'm fairly certain the issue is electronic, but if it's mechanical (ie torque converter) I don't want to spend $500> for a tune on a trans that needs parts replaced or rebuilt. Just wish I knew the cause before spending the money. From the few things I've read though a tune is probably the next step. Either that or the Range AFM delete box. Do you remember which tune you went with?

Any other things to check?
 

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If the issue is V4 causing the delay, then yeah the Range would likely help. I am inclined to believe that if the dash says your in V8 when this happens, then V4 delay isn't the issue. I feel my truck had a delay more so than now with the tune. A tune helped my truck too, but I had different complaints. A lot of folks go with Diablo and some go one step further and do a custom Diablew tune. Black Bear is another popular option. I went custom Lew tune since for one, the product was a good fit for me and Lew is a member here so it is real convenient.
http://www.diablewtune.com/
 

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2010 GMC SIerra All Terrain C.C. 4x4 5.3
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Yep...I have a Diablosport I2030 and the Lewtune also. From my understanding...the custom tune cost of $150 is really cheap compared to others. And you get free updates if you change things for a year...then can pay a little less for updates down the road if needed.

I purchased a used tuner for a good deal. You can also get one from Lew and it is discounted a little...but you are easily up near $500 doing the new route. I have a total of $350 invested in my tuner and custom tune.

I recall mine hesitating when downshifting or hesitating to even downshift maybe rather. But the worst was if you were driving slow in traffic...let off the gas then got back on if if traffic started moving...seems it really would confuse the trans and it would jam into a gear and I always hated that. The custom tune fixed that. And got more power(a little) and it feels so much more responsive. So much so that I hate driving my wifes Pilot....haha
 

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+3 on a Diablew tune. It makes all the difference in the way the trans shifts. No more bogging down in too high of a gear at low speed and having to floor it to get the truck to move. As Neal said, it's way more responsive and drives like it should have from the factory.

Try the M5 thing for a few days first to see if it's AFM related.
 

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Discussion Starter · #8 ·
Thank you all for the help. I'll test out the M5 for a bit then more than likely go with the Diablew tune. Hopefully he's got good instructions lol. I'll come back on & update as things progress, but may take a few weeks before I get to the tune. Thanks again
 

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Discussion Starter · #9 ·
Have driven it in M5 the last few days. In M5 it does not stall and jerk into gear. In M6 it will. I've noticed though it will only happen when it's downshifting 2 gears - not just 1. If I really hammer it, and it drops 3 gears....I think(?), it won't have the issue then either.

It seems to only be doing it when it's dropping 2 gears from 6th to 4th. If it drops from 6th to 5th there is no issue.

Oh, @Neal, you were right - the hesitation/pause period was excessive in my mind. It's only about 1 second or a hair over.
 

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2010 GMC SIerra All Terrain C.C. 4x4 5.3
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I believe a lew tune will fix you up. It is pricey just for that...but most everyone on here who has gotten on...have been very happy with it and feel it is worth the cost.
 

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Discussion Starter · #11 ·
Ok, thank you. It might be 2-3 weeks, but the Diablew tune will be my next step. I'll update as things happen. Thanks again
 

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So, I've been having the same EXACT issues with my truck. Currently ~190k on the truck. I've even had the transmission fully rebuilt and that fixed the issue for maybe 20k miles, but it came back, and it seems to only get worse over time. Using tow haul mode or manually shifting to drop gears and pass on the highway seems to be the best way to "drive around" the issue. But it's very frustrating, and in poor traction conditions can even be dangerous.

It is definitely an electronic confusion. The trans has no issue dropping from 6-4 if I manually shift it, but applying medium throttle in D and the transmission hesitates, then shudders/slamms into the lower gear like a teenager who doesn't know how to feather a clutch. Heavy acceleration dropping from 6-3 doesn't seem to have any issues. It's always the 6-4 drop.

I wish somebody could tell me what's actually wrong with it. I'm tempted to try a new transmission instead of rebuilding, but if it is a computer or electrical issue, I don't want to throw good money after bad.
 

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Hello, I joined this group after reading this post resulting from my google.
I am hoping that the member that started this tread would post an update to any resolution? My 2012 Sierra 1500 5.3/6l80e is doing exactly the same thing. Hoping that I could get some additional information.

Thanks, Randy
 

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Did anyone ever figure this out? I have the same 6-4 downshift problem on my 2012 Silverado 1500. Just like the keystone kid's post, when in manual mode it doesn't happen. I'm hoping to get some good advice before I throw any money away.
 

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Doubt the OP will respond to any of you, unfortunately, it has been over 2 years since his last visit.

I recently have had a similar issue as some of you are describing. At 40-70% throttle, when shifting from 2-3 gear or 3-4 gear, it keeps a constant rpm but right before shifting is surges 500rpms or so and then slams into gear hard enough to chirp the tires.

This is what a circle D converters specialist told me.

"It couldn't hurt to go ahead and change the converter if it has 155k miles. This is generally when the lockup clutch linings start to fail.

That being said, I would personally get with a tuner for some diagnostics. If the shudder you are experiencing is converter lockup clutch related, you should pretty easily be able to turn lockup OFF in the tune and take it for a test drive. If you still have the shudder, It would likely be time for a trans build."
 
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