4.0

definitely annoying
Typical Repair Cost:
$10,250
Average Mileage:
122,600 miles
Total Complaints:
1 complaints

Most Common Solutions:

  1. not sure (1 reports)
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2020 GMC Sierra 1500 transmission problems

transmission problem

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2020 GMC Sierra 1500 Owner Comments

problem #1

Dec 062023

Sierra 1500 AT4 3.0L I6

  • Automatic transmission
  • 122,551 miles

A D V E R T I S E M E N T S

I have always driven a GMC since I got my license at 16 but I never would have thought that the quality of the actual trucks could diminish like they have over the years. I love the brand and I have always loved the look of a GMC truck but if the mechanical problems and quality of parts keep going downhill I might have to switch.

When I heard that GMC was making a 1500 diesel Duramax I couldn't wait to get my hands on it. Just for the simple fact that I knew it would get great mileage which it does and the value retention that diesel motors have is a bonus within itself. and it was GMC with their Duramax engine and Allison transmission combo you cant beat them.

I bought this truck brand new with 5 miles on it and before I bought it doing my research, I had heard horror stories about the new 3.0L Duramax engines having terrible transmissions across many forums and chat rooms. Even with transmissions blowing at 20k, and 40k miles.... well mine lasted to 122k which in my limited but reasonable understanding of vehicles is ridiculous, especially for a Duramax/Allison combo....

To my problem, driving home one night on the highway in cruise control doing about 70. I looked down and needed fuel, so I pulled over to an off-ramp, and all of a sudden an audible grinding started under the center console of the truck. The truck drove fine into the dealer still grinding, but shifting and moving fine. Turns out that it was a gear from the internal transmission pump that had sheared off and spread metal shavings throughout the transmission therefore leaving me with a 10k+ bill to replace the entire transmission.

- alexj1494, San Antonio, US

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