nluchau

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.

Update: Transmission was replaced under bumper to bumper at 33xxx miles. I am still noticing harsh downshifts but not as bad, one other thing I noticed is the transmission is trying to get into the highest gear so darn quick. At 32 mph it will go into 5th gear?!?!? I've been told to give it 3k miles to have the transmission learn my driving. Still doesn't feel right to me.... I now have 35xxx.

Thanks for the replies so far. Much appreciated! Is it worth it to have the adapts reset or see what the dealer can do? Maybe another fast relearn perhaps? Not planning on going the tune route at the moment.

Dealer just recently put a reman 6 speed in my truck with 34k miles. Back story, I was having hard downshifting (jerky) and now that cleaned up a bit but what I am experiencing with the new transmission is this: If I accelerate slowly and hit about 32mph it upshifts with almost like a thump. If I accelerate faster it upshifts at about 40 just fine and feels normal. My observation is, its trying to get into the higher speed too quickly. Anyone experience this and is there anything the dealer can do for this? Is it still learning??? Thanks!

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

Same thing happened to my black truck and it was indeed bird crap. It ate through the clear and clay bar never did anything. Had it polished out but can still see where it was. This was on my 2016

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.

Hey bud, was your's doing the jerks or was it actually clunking? Can you refresh me on exact symptoms again? Thanks!

I know I beat this like a dead horse but I'm at now almost 31k miles and still experiencing the downshift jerks when slowing down. I feel them at 5-4, 4-3, 3-2, 2-1. It almost feels like a tie up of gears or someone tapping the brake when it occurs. I've had the taps reset a couple of times and also the valve body replaced. Nothing has fixed it. Also I feel a lunge or surge sensation on occasion when slowing. I wonder if that is the torque converter is releasing???? Word is the torque converted is locked during Decel and unlocks and locks at each downshift. Does this sound correct? Is this still normal characteristic or has anyone gotten theirs fixed under warranty? I've tried M5 mode, I've tried turning off grade braking, nothing has corrected the issue. Thanks!

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.