I've had my Range DFM disabler for a week now. In mostly in-town driving, but with some expressway driving in DFW, I've noticed a massive difference in feel, response, throttle, and even transmission consistency. I've got a 5.3L with 8-speed, and I finally feel that it's being used for why I bought it. It's noticeably smoother as well. So far, there have not been any hiccups or issues, and the mileage loss is barely noticeable for me (thus far, at least).
It's like I have a whole new truck, and as an added bonus, I no longer have to hit the Start/Stop button when I start up my truck. 5/5 so far!