wmadden

You’ve got the torque converter slip. I have it on both my vehicles. I’ve had the flush, the valve spring replacement, new engine mounts, and they replaced the TC. Still an issue. My dealer said they are working on designing a new TC and will replace via recall. Don’t hold your breath.

Not to bum you out, but I went through the same paces to include a new TC. Still shudders:-(

Thanks @SILVER SLED . Really wanted a handheld to take the truck to stock before taking to a dealer, but I guess custom is the only route at this point if you want to tune the 8 speed? How has your truck performed with the i3? Seems like a lot of guys rave about Black Bear, but I've done the custom tune thing before and I don't know if I'm committed enough to wait and work the process it takes to dial in the tunes.

Anyone use the Diablo Intune i3 on the 6.2 with 8 speed? Results on shifting? I've got the 1200-1800 studder and am hoping cutting off AFM and firming up the shift points will get rid of it.

Which programmer did you end up using?

Thanks @Bart’s Silverado . Spoke with Morgan at Performance Driveline, who provided me more information about this issue than three dealers. Basically, the two piece drive shaft, as Bart's Silverado explained, eliminates the critical speed issues most of you are having with the one piece aluminum drive shafts. They're also stronger so they'll take more HPs. My issue, with the studder at 1200-1800 rpms they believe is due to a batch of mis-machined axles from the manufacturer that GM installed in these trucks anyway. They have a truck in the shop with the chevy shake and the studder my truck suffers from and they've tried everything from tires to drive shaft, which fixed the critical speed issue, but not the studder. They've ordered some custom axles in hopes this will be the final fix. The estimated cost will be $550-600 for the custom axles. She said they'll have the axles in at the end of the month and should be able to report on the results then. Morgan isn't the owner, but she was extremely helpful and knew the issues inside and out. When and if you decide to upgrade your driveline, give these guys your business. Class act operation.

Agree @Bart’s SilveradoI'll bet a reflash to a performance tune would clear up my issue. Does anyone have experience with defending warranty coverage after reprogramming, changing out the driveshaft, tires, rims, and/or shocks? I would think you'd be SOL if still within warranty. That's the only thing keeping me from taking the matter into my own hands at this point.

Sounds like there's a "fix" for the high speed shake... has anyone overcame the acceleration studder at 1200-1800 rpms? Other than selling the truck?

Didn't work for either of my vehicles. In fact, on my Sierra, they flushed the tranny and it was worse after I left the dealer even though they reported to me that it was fixed.

On our '16 Yukon XL Denali (60k miles), we noticed the shimmy at 80 mph when cruising down the interstate. Started first with checking the rims and sure enough, all 22" rims had some sort of out of round condition. The dealer had a matching set of 22s in stock with factory wheels that we had to purchase for $3000 and that fixed it. Then came the drivetrain shudder at 1200-1500 rpm when at speed (50-60mph and coasting in 8th gear with AFM engaged) and the engine AFM is switching from 4 cyliinder to 8. Both my Yukon and Sierra have this studder, which feels exactly like a slipping torque converter. I've taken my Sierra (17,000 miles) to the dealer 5 times since 14,000 miles now. They replaced the engine mounts, fixed a broken valve spring (wtf), flushed the tranny, replaced the torque converter, and reprogrammed the ECM to learn mode. Both vehicles have the 6.2L with the 8 speed tranny. I've driven them in manual to override the AFM and it doesn't seem to help. It seems there are multiple issues, both electronic and powertrain-wise going on and I'm not confident they'll get it fixed. There's a lot of ideas within this thread in how to fix with aftermarket parts, but it seems there are varying differences in what exactly each vehicles studder/shimmy/shake is. I've been a die hard GM owner due to their reliability and I just think the quest for getting too cute in winning the mileage game with competitors has made the future of GM trucks an unreliable risk I'm not sure I'm willing to take, especially at the price tags we're paying for these vehicles. I wish I had just kept my '06 Duramax and drove it into the ground.

Okay, so we're 797 pages into this thread and GM obviously isn't going to do anything to fix the problem... I have two vehicles, '17 Denali crew cab and a '16 Denali Yukon XL both with the shimmy/studder. How many of you are planning to trade in for a '19 with the new design, or are you done with GM and going another brand?... and if so, what are you looking to move to?

Yes, I can do that to make it not happen, but what is the permanent fix? It's got the clunky 8 speed tranny. I'm not sure I know how the AFM is engaged on these trucks.

Thanks to everyone for posting so much information on the "GM shimmy". My wife's 2016 Yukon Denali has it and this has helped. My 2017 Sierra 1500 Denali has a different problem, however, and I wasn't able to find anything in this thread about it. When under power and at speed, if you're at 1200-1800 RPM and accelerate, the truck violently shutters. I would've bet money that it was the torque converter based on the feel. I've taken the truck in and sat the tech in my truck to duplicate. The repairs so far have been 1- new engine mounts, 2- one of the cylinders threw a misfire code so they found there was a broken valve spring (wtf?), 3- flush of the tranny system (GM requirement), 4- replace of the torque converter. I was pretty sure the new torque converter would've fixed the problem, but guess what... it's still there! At 14K miles, I'm super disappointed. I believe it may be the fuel management system or something switching from a 4 cylinder mode to 8. I am at a loss and so is my dealer. Thanks in advance if you have any guidance here, but after 25 years of being a die hard GM fan, this has me doubting.