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2020 2500HD Transmission issues

gpraceworks
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Bigcountry70 New Member

Bigcountry70

Posted
Posted (edited)

2020 GMC 3500 Denali DRW.  Mine is going on Day 2 at dealer.  They have no clue.  My issue was while backing in 5r.  Same email from Onstar!!!  I have to be out of our campground Friday.......my 2016 GMC never had a problem.  I wanted 360 camera!!!!

Edited by Bigcountry70
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Rodney Goins
Rodney Goins

2- 2023 duramax trucks both less than 60,000 miles one was in shop for month 2nd one still in shop over a month and waiting. Have driven 6 speeds never touched with milage in the 500,000 miles no prob

  • 4 weeks later...
bryant87 Enthusiast

bryant87

Posted
Posted

at 17K miles i noticed my truck leaking from the transmission, brought it to the dealer, they originally told me it was the seal, but once they pulled the transmission to change it they noticed a groove cut in the bell housing that was causing the leak, they ordered a new transmission, took three weeks for the allison to come in, came in Monday should be picking it up on thursday.

migrabill Enthusiast

migrabill

Posted
Posted

I've got a 2020 2500HD Denali Diesel with about 3k miles on it. I would say one of the things I like the most about the truck, so far, is that 10 speed transmission. Shifting is seamless, so far.

  • 3 weeks later...
PlotResearcher New Member

PlotResearcher

Posted
Posted

I received my 2020 in January. The dealership installed the gooseneck hitch with around 500 miles on it. This exact problem happened when I was leaving from the parking lot immediately after the hitch was installed. They reflashed the firmware for the transmission and it was fine for 6000 miles. 
 

Then after a long week in May of towing 17,000 lbs it happened on a Friday night with a 3 hour drive to get home. That week alone it had worked flawlessly and it was a sudden hiccup. No warning signs at all. Seems there should be more functionality of the on board diagnostic system than just a “check engine” light. 

  • 1 month later...
Christopher Zlamal New Member

Christopher Zlamal

Posted
Posted (edited)

My 2020 Z71 4x4 Diesal with 1800 miles in the dealer for extreme hard downshifts feels like being hit from behind from 5th to 4th abd 4th to 3rd ??   dealer told me thet sent infor to GM and it could either sit in my driveway or their lot until someone contcts them ????  really???  74k sticker price had truck 10 days and 1800 miles Im screwed ??? 

Edited by Christopher Zlamal
bryant87 Enthusiast

bryant87

Posted
Posted
2 hours ago, Christopher Zlamal said:

My 2020 Z71 4x4 Diesal with 1800 miles in the dealer for extreme hard downshifts feels like being hit from behind from 5th to 4th abd 4th to 3rd ??   dealer told me thet sent infor to GM and it could either sit in my driveway or their lot until someone contcts them ????  really???  74k sticker price had truck 10 days and 1800 miles Im screwed ??? 

Had this happened to mine, first transmission I had to change at 16k miles because of an unstoppable trans fluid leak then the new replacement trans had a hard downshift from 4th to 3rd, but a started doing a manual downshift at higher rpms a few times and it stopped, it would only happe. When the trans was cold so thinking it was just tight machining tolerances 

Dunn Senior Enthusiast

Dunn

Posted
Posted
On 11/25/2019 at 6:34 AM, SkidooSteve12 said:

 

My 2020 Gasser with the 6 speed has had a couple of weird feeling shifts, but overall very nice.

 

I did see a 2020 2500HD on a flatbed Saturday at a corner and saw that they followed me and pulled into the local dealership. Curious what the problem was with that truck... didn't see if it was a gas or diesel, but I'm guessing a diesel as they mainly sell diesels there.

I as well have had a few weird shifts....it is brand new and I don't get spooked too easily so well see what happens, only at 2k miles so just breaking in still....it is smooth when driving

IMANOD New Member

IMANOD

Posted
Posted

Just got my 2020 Duremax and took it camping over the weekend. It rained on us and I ended up having to put it into 4 low to get out. The transmission made this horrible noise as soon as I put it in to park. It would only happen going in to park while in 4 low. Dealership has no idea what is going on. There is an identical truck on the lot that has the same thing happening. Not even 500 miles yet, so I hope they get it figured out.

honda65 Enthusiast

honda65

Posted
Posted

Following this topic.....I have 1100 miles on my 2500 HD TD and while it seems to shift smooth, there are some new sounds that have emerged. Plus sometimes there is a clunking noise that seems to come from the rear, hard to pinpoint. We are getting ready to hit the road for a month worth of travel pulling a 31ft travel trailer, sure don't want to have to stress over stuff

gpraceworks Enthusiast

gpraceworks

Posted
  • Author
Posted

Original poster here. Back with a new update. 

Trans related repairs so far on my 2020 AT4 2500  Diesel. 

 

1. 300 miles trans limits me to 40mph siad fluid was low. Fix: Top off fluid. 

 

2. 1100 miles  Same as #1 symptoms but limited to 20-30mph. Fix: Replaced trans valve body.

 

3. 2000 miles Same as 1&2 symptoms. Fix: Replaced entire transmission.

 

Now for the most recent update. At just north of 8000 miles truck starts bucking back and forth like if someone grabbed you on your shoulders and shook you back and forth. No codes, no warning lights, no OnStar emails. Took it to the dealership on Monday. They can't figure out what is going on.

 

I called and asked them to send me all the service records (9 pages). I used the term Lemon Law since I talked to a lawyer. 

Low and behold the service manager calls me with the service agent I've been working with and starts asking me how I've been using the truck. (Felt like they where trying to make a case). They even asked the make and model of my camper, how much is weighs. "Well let's see, I'm using it for its intended purpose. I tow a camper that weighs 11,300lbs a total of 4 times with the longest trip being 1.5 hours and the other 3 around 20 minutes locally". 

 

Now they are going to replace the transmission for a second time. 

 

I love the look of this truck, but I'm running out of trust and patience. The above only covers the transmission issue and not the recalls and other issues. It will be over 30 days if been without my truck by the time I get it back. They need to give me a new truck and junk this one!

  • 1 month later...
Timothy Mortson New Member

Timothy Mortson

Posted
Posted

I have a 2020 1500 Silverado. Currently in the dealer for transmission problems, 2nd time.  Any time I go to tow anything after a few miles it will not shift out of 4th gear. The 1st time in they replaced "transmission high pressure fluid sensor", it was showing "stuck on fault'.  Also replaced the valve body and reprogramed the computer???, what ever that means or entails. Got it home and within 2 days I went to haul my sons boat, a 23 foot ski boat, and the tranny started acting up again, doing the same thing it was doing.  Hopefully they get it right this time. Thankfully its a lease, but I feel bad for the poor guy that buys it after me.  4 cylinder with a turbo, and probably will not hold up.

Njmurvin Enthusiast

Njmurvin

Posted
Posted (edited)

For you guys with transmission fluid leaks, what color is the fluid? I noticed a drip or two on my garage floor located at about the center pillar between the doors. I'm used to trans fluid being pink. This looks more greenish/clear. Being so far back, I was thinking maybe the transfer case ... but after reading this thread I'm now wondering if it could be the trans. Regardless, it will be going to the dealer later this week. Performance wise, it has been solid. But I only have 980 miles on it - of which about 300 were fairly severe towing.  Shifting and e-braking both up and down Big Bear Mountain was flawless.

Edited by Njmurvin

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