If you think AFM is a marketing gimmick, you need to think again and try it out.
AFM out of the box will return 10-15% better MPG in real world conditions.
By virtue of a tune, it can also be cranked up to return even better MPG.
Why is it in the auto?
Automatic transmissions are less fuel efficient than manuals.
It has to do with gear ratios, manuals have that low-geared 6th gear for optimum MPG.
Without AFM, the automatic may have had a gas guzzler tax.... the EPA ratings would've came in around 14 city / 22 hwy (my "guesstimate").
It would not shock me in the least to see a tuned L99-equipped Camaro get 28-29MPG highway... with no other modifications other than a tune.
Is the tune necessary? Absolutely not.
Even out of the box it's rated at 25MPG, which is darn impressive!
Additionally, the operation of AFM is seamless and silent.
You won't even notice it turning on or off.