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I have a 2020 GMC Sierra 1500 5.3 with less than 12 K miles I have had it in for the problem 3 times. I am told there is nothing that can be done to correct it. Here is the problem,  at any speed (especially highway speeds) a vibration occurs frequently, it only last a few seconds but a mile or so down the road it will happen again. This happens on flat roads hilly roads and can really be felt on smooth roads. The last time I had it in the service department they said it is happening when the engine changes from 8 to 4 cylinders and back to 8 cylinders and that there is nothing that can be done to correct it. It is hard for me to believe that GM has built a vehicle with a very annoying problem and it can’t be corrected. I am thinking seriously about putting signs on the truck that says (DON'T BUY GMC TRUCKS THEY CAN'T FIX PROBLEMS WITH THEIR MOTORS). I paid way to much for this truck to have to have to go down the road with it vibrating and shaking, very annoying!! Anyone else have this problem and does anyone have a suggestion how to correct it?

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  • 1 year later...

It sounds like normal AFM/DFM operation to me. I run our DFM-equipped 5.3 in L7 (8-speed transmission) to disable DFM and it's a much smoother, better driving experience. I still get 21 MPG on the highway in 7th gear (3.23 read end) so you do lose about 1-2 MPG, but not bad.

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The way i see it is they're pulling your leg. GM has had cylinder deactivation for years now and haven't ran into that problem. There are many tsbs and have ran into many low mile gm truck having motor mount issues. Along, with torque converter problems that causing vibrations  

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46 minutes ago, It's Tim said:

Why is everyone so quick to blame the manufactuer when EPA/CAFE mandates caused this? 

Because the manufacturer builds and makes the design not the EPA/CAFE. 


Also I believe you are incorrect, GM did this to help the fuel economy back in the early 2000s, no mandates caused them to create cylinder deactivation. They were looking for ways to try and keep fuel economy good on trucks and SUVs to keep up profits. 


Interestingly enough though this started in the 70s in a Cadillac and the whole idea was scrapped after a year because it was so difficult to keep functioning. Nowadays it works but it is still a weak point. In the 70s it was actually a gasoline mandate that caused them to start thinking this way.




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Was having the same issue and was diagnosed today with a torque converter problem and they are warranting me a new one. Search up TCC shutter on here. Theres other possible fixes for this

Edited by Rob133
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  • 5 months later...

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