nluchau

No check engine light.

Thanks for the reply rlcole321, I am using a range so its kept in V8 the whole time. I get what you are saying about it hanging around that 1k rpm mark and you are correct. Once at that point in 4th or 5th gear and I tip in to accelerate I notice the chuggle. Knock on wood I never felt it so far today yet after filling up with 91 octane. I did clean the throttle body today too. I'll report back if it continues to occur once running 91 through for a while.

I just started noticing this after an 1100 mile trip. A little history: Transmission and Torque Converter replaced at 35k. All updates done. After operating temp is reached on vehicle and from a stop. I accelerate until it hits about 4th or 5th gear (typically 40mph) and then do a tip in of the accelerator to increase speed although I don't want it to upshift. I notice its almost like a misfire or chuggle feeling like its starving for fuel. That is until I kick it down and it upshifts and then it won't do it. Just does it under light throttle tip in. The trans fluid is nice and red, I replaced the air filter and put a bottle of techron in for now and topped it off with 91 octane. It only seems to happen once at operating temp. No check engine light. Just curious if others have experienced this and what the solution was? On that 1100 mile trip I had to fill up a few times using 87 octane since I could not find 89 that I usually use. I am hoping it could be bad gas but not totally sure. Any ideas greatly appreciated.

If it matters any, I just brought my truck in for the same reason. Since new (2016) its at 210 (195 degrees officially). Since last October its been 1 notch below what I call "normal". The service advisor took my truck in and they put the PET scan tool on it and even called up GM. They said it was completely normal and no issues. Well I know my pickup and know it is definitely not normal. I talked to the service manager (who I know quite well). He made a phone call and in moments notice I was in a loaner vehicle for the night and they would have a new thermostat in the next morning. Low and behold I got a phone call the next morning to come get it and its back to normal again. This exact issue is more often than none a thermostat issue if anyone deals with it.

Interesting! Why would they replace the pads then if it doesn't remedy the issue? Note: The pads were on a later revision of the Service Bulletin also.

I had inserts put in about a month ago, noise went away initially but is back now. What gives???? Question, how many new inserts should I have put in? 2 in front and 2 in rear? Are they indeed gray vs black so I can easily tell if I look at the springs?

Same on my 2016 with 41k miles.

I noticed this from day 1 of ownership (New truck). Now I have 39k miles. On my second transmission and it still does it but not as bad. Now I have an abrupt 4-5 shift under slow acceleration. It hits hard at slow throttle but if I'm heavy on the throttle it seems ok. At the moment that is now more irritating to me than the jerky downshifts.

Thanks for the honest feedback on the product. I guess I won't be trying it. Funny thing is though, my downshift jerks aren't random as they occur all the time.

Good question, as far as I know the dealer was only replacing the fluid in the 8 speeds not the 6. If you switch it out on your 6 speed let us know if it works.

I've always wondered about this stuff and had heard good things. I just wanted warranty to work for me but it hasn't. Might be something I need to try.

My lockup isn't harsh or jerky either upon acceleration. The only issue is upon decel when it goes 4-3, 3-2, 2-1. There is a tie up sensation when it downshifts and what I've read and been told is TCC is engaged during decel and at each downshift it unlocks and locks again but yes I do feel the "let go" at almost stopped and it feels like someone bumped into you from behind. If the TCC wasn't locked up during decel I dont think I'd be bringing up this issue but apparently its just how it is. It's really hard for me to acknowledge this I guess.

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...

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

Funny you mention that: I've noticed if I'm harder on the gas before slowing my downshifts are way more desirable yet almost normal feeling. If I'm easy on the gas the downshifts are harsher when slowing.

Interesting and great info here mmmikkke! Thanks for this write up and yes I think this is the concern with our trucks and downshifting. I had my transmission replaced under bumper to bumper and it still does it. Now it goes into 5th gear at 32mph. I think this is a bit much. Let me know what your outcome is here.

Do you mean the 8L90 and not the 6L80?

Yes you need to disable grade braking at every turn on of the key and sadly this did nothing for my deceleration downshifting.

Duplicate post

I dont know if the dealer has ever done a clutch relearn on my 6L80, is that a thing if they reset taps they can do that? I know on the 8 speeds they reset them and relearn but I hear nothing about the 6 speeds. The TSB that talks about the 8 speeds having harsh 3-1 downshifts is exactly what I am experiencing with my 6 speed but it seems my issue falls on deaf ears. This is what I am referring to that doesnt pertain to my issue but I'm having almost the same issue. https://gm-techlink.com/?p=7170

Mine has this 2-3 hard shift (first one of the day) too. Then its fine.

My valve body and TCM was replaced already and the taps reset a couple of different times but that was all. I believe with the valve body the fluid was mostly all replaced? It's almost like its downshifting too early thus causing the rapid jump in RPM and the jerk/braking sensation because its not matching the speed.

Good to hear from you again njk4o5! Mine isn't downshifting where I'll spill something. Its just annoying as heck still.

I just found this online: https://atracom.blob.core.windows.net/webinars/gm/6l50_80_90_updates.pdf 6L80 Intermittent Harsh Downshift, Chuggle or Shudder During Deceleration 5.3L Tahoe, Suburban, C/K Trucks Customer complaint may be harsh forced downshifts or the chuggle/shudder during a coast down intermittently. This is considered “Normal” with this powertrain package. It is a self test for the O2 sensors. Test runs with the vehicle speed above 45 MPH (72 kph) in 6th gear with the TCC applied. The ECM drives the fuel system rich and then into deceleration fuel cutoff mode (shutting the injectors off) to check the system. Test will end during the deceleration and fuel is restored. (This typically causes the Shudder/Chuggle shift feel in the vehicle). Aggressive throttle response during this system check mode will cause the vehicle to have a “Harsh” downshift (this happens because the TCC remains applied during the test). If the test runs while in 5th gear, the TCC will not be applied and the complaint will not likely occur. Note: The test is designed to occur one time per key cycle, but can run up to 10 times if aborted due to throttle input. Mine isn't intermittent as it does it all the time, it doesn't go away in M5.

Are you guys experiencing what I am specifically? When I go above 40 and coast or easy brake to a stop. When its doing the 4-3, 3-2, 2-1 downshifts I feel a jerk or a tie up sensation and a release when it downshifts. I also see the RPM's bump up (which is what I should see). The jerks or bumps or tie up sensation feeling has been occurring since new on my 2016 5.3 6 speed. I've brought this up quite a bit here but there tends to be no fix insight. The dealer replaced valve body and TCM and has reset taps but nothing has fixed it.