6L90E (gas truck) 2-1 downshift CLUNK

[Justin Keller]

It's been in many times.  It's "normal" and it's and out of warranty. 

[Luke Jenkins]

I've been having a very similar issue and struggling to get chevy dealers to resolve it.  Here's the details that I have in other online forums with videos I put on YouTube of the clunk.  Its been a nightmare and trucks been in shoo for months of the last 6 months.

 

The issue with the transmission happens where a large clunk/jolt can be heard and felt in the body of the truck and the whole transmission shakes (I have video proof from under carriage and in the vehicle). This happens when the truck downshifts quickly going from 3rd gear (~40 mph) and slowing down and downshifting to 2nd or 1st gear (around ~15 mph). This happens every time I drive it, and is easily reproducible. I have also experienced the issue occur occasionally at different speeds and accelerating, but the downshift method is the most consistent way to reproduce.  Note that coming to a slow stop doesnt do this and truck drives and shifts gears well in most conditions.  But coming to a quicker stop is very reproducible.  See videos I recorded below of the issue.

 

Transmission Clunk from Undercarriage video: 

 

 

Inside truck #1: 

 

Inside Truck #2:

 

 

 

I have a 2021 silverado custom trail boss with v8 engine and 6 speed auto transmission.

 

Its been in 2 different chevy dealers with this issue for the past 6 months. I first dealer agreed it was an issue, replaced a bunch of faulty parts in transmission (including torque converter, tbv, housing, Filters, valves, and white paste was found circulated throughout transmission), but didn’t resolve the issue at all and then told me to ignore it and that it’s normal behavior and working perfectly even though I showed them the same issue was still occurring. I took it to a second Chevy dealer and similar thing happened, where they agreed that it was an issue and that the transmission was not working properly, and found torque converter to be bad (even though the other dealer just replaced it and claimed it was perfect) and metal shavings in the transmission fluid, and now changed stance telling me the clunk/jolt transmission downshift issue is normal behavior now in these trucks and not a concern.

 

The first dealer was AutoNation Chevrolet West Colonial in Orlando (very poor customer service, kept my truck from 5 months, very rude manager and director who have no business being in management or customer service or representing GM/Chevy, and  and gave me false information). The second Chevy Dealer is Carl Black Chevrolet in Orlando. No complaints about them, theyve been reallybcaring and professional but the issue still isn’t resolved and I’m being told now that the same issue from when I brought it in is now deemed "normal" which I’m struggling to believe with all the evidence against that.

 

I opened up a GM corporate claim, but they haven't helped yet.

It is very concerning why it is having all these transmissions issues that should never have occurred in this new of a truck. I'm worried that whatever is causing this clunk is causing the parts to fail.

 

Any advice from anyone here?

I don't feel like I'm being given any other choice but to sell it or keep driving it, since GM wont fix it.  With all the proven issues my transmission has had in last 6 months, I want GM to offer me an extended transmission warranty or replace the seemingly lemon transmission with a new one   Doesn't make me feel confident in the Chevy brand or taken care of as a customer.  

 

@Epsilon Plus

 

Thanks!

 

Edited May 22, 2025 by Luke Jenkins
Typos

[Luke Jenkins]

On 3/19/2025 at 8:29 PM, Justin Keller said:

It's been in many times.  It's "normal" and it's and out of warranty. 

@Justin Keller Sounds like the same scenario I've been struggling with.  Very concerning and frustrating.  (See my post above if interested)

Edited May 21, 2025 by Luke Jenkins

[Justin Keller]

I just switched to Amsoil and deleted the thermostat.  It might be slightly less harsh but still there.  

[Epsilon Plus]

I added a Pulsar LT for tire size massaging. It's also a throttle massager like the Pedal Commander. On level 3, 30% more response than stock, not only does it make the truck feel like all the advertised torque is actually there, improves the heck out of response and drivability, but it lessens the clunk quite a bit. Probably because it is still under a bit of throttle on the dump.

[AmericanPie]

On 8/22/2024 at 8:34 AM, GO-N-KR8Z said:

Well Sorry for the late question to this thread but, was the outcome with this issue?

I own a 2022 that has 20k on it and it has been back to the dealer twice. They keep saying this is normal.

2-1 down shift wants to rip the rear-end out sometimes.. My passengers think I am brake checking them.

anyway, just trying to figure out a direction. Thanks

Sorry it took so long to reply.  My long term experience following the high mileage 6L90E trans flush is good to date.  I've put approximately 14,000 miles on it since the flush, and the hard downshift, and clunk is 99% gone.  On a rare occasion I have heard/felt it, but it was almost imperceptable.   I may do another full flush after I hit 20,000 to 25,000 following the first flush.  It depends on how the trans feels.  As of this writing,  it upshifts with certainty and downshifts smoothly.   It has about 114,000 miles on it, but feels like a fresh transmission.  One last thought....I used the correct full synthetic, Dexos rated, Valvoline brand, trans fluid for the flush.  I wonder if that had anything to do with my success?

 

FYI, at 94K GM warranted a new L8T engine, as it threw a rod.  I may have addressed this issue elsewhere in the site, so I won't go into detail other than it was covered up to 100K because it was originally a Fleet Purchased vehicle and the new motor is awesome!  Bravo GM!

Edited August 17, 2025 by AmericanPie
Added info