The device does what it says. It disables the AFM and takes away the hesitation and the sluggishness. I used to have a 2005 NBS Tahoe and I regretted exchanging it for a 2013 NNBS Tahoe due to the sluggishness caused by the AFM. Now I am enjoying the newer truck due to more responsive throttle. I did notice a loss of 0.5 MPG but it's worth it for the truck to not feel like a big slug.
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I am up one mpg after one month of owning the range AFM disable and I also love the on demand power my Sierra was meant to put out. Not to mention this has also fixed a few hard shifting issues as well!! Thanks Range! Looks great too, has a cool looking blue light and looks very clean.