How to tell if AFM is active?

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Saltydog

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Wow I also have a 5.3 on my 2023 Yukon slt. How do you get such good mileage on the hwy? I think the best I have gotten is around 24mpg driving around 60mph. I generally drive very mild (no harsh acceleration and lots of coasting).
I have seen about 29 MPG with 21 Yukon 5.3, normal Highway is about 24-26mpg.
 

Saltydog

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I have enough seat time in our Yukon and I can tell by the throttle response and the engine/exhaust sound when DFM is active.

That said, GM did a very good job of masking the sound of it.
 

B520044

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you should be able to feel it and hear it, it drives me absolutely insane.
Drives me crazy too. I feel it more than anything. To me its like driving a manual transmission in the highest gear when going 40mph.
 

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