Just wanted to chime in on my expereince and opinion on the AFM.
Mine will regularly shift into V4 mode on the highway when I have it in cruise in the 55-65 range. Above 65 it likes to stick more to the V8 mode. Shifting between 4 and 8 is seamless but not completely undetectable. It could also be the truck shifting to accomodate the drop/increase in power but a passenger wouldn't know the difference. The instant gas mileage display can jump up past 20 easily when it dives in V4 mode and have had strictly V8 trucks in the past and from what I can tell the display seems accurate.
I've read of products users have recommended on this forum that you could plug in to force it to stay in V8 mode. Keeping in V8 serves no purpose for me. I'd actually like to see a product that could keep it in V4 longer. A family member has a 2011 GMC Terrain with an ECO button. It's already a V4 so I assume it plays with the RPMs/Transmission in her vehicle. It definitely feels sluggish when pressed but for me, I'd accept the sliggish performance for highter fuel economy as long as I have the option to disable it when I want the performance restored.
Other vehicles out today have the ability to switch between driving modes. Ideally I'd like to see a Sport mode which would keep it in V8, Normal mode which would be the stock setup we have now and an Eco mode which would push it to use V4 mode more often than V8.
AFM system has been great to me so far, but the addition of something along the lines of a 'Mode Selector' would really take it above and beyond.