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2014 ATS 3.6 Premium RWD, 2016 Corvette Z06, 2018 GMC Sierra Denali 2500HD Diesel
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As Melze noted, the programming of the 3.6 and 6L45 transmission in the ATS will result in it shifting very early under certain conditions causing light "spark knock". My 2014 ATS RWD 3.6 premium trim will do this on moderate upgrades at slow speed, I just paddle down a gear to stop it. It is part of the fuel economy programming. Fuel on the margin of meeting the 87 octane rating along with degraded spark plugs and/or coil packs will make this problem more noticeable.

I also have a 3.6 in my 2021 Camaro RS but the powertrain programming with the newer 10 speed auto is far more refined and it never has showed that quirk like the ATS.

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