OK, I have a Derringer, Pedal monster and Big Ass air cleaner, data monster and super gauge. I performed detailed before and after mileage studies to see the effect. I ran a tank of fuel driving the truck normally with all the Banks setting at stock parameters and noticed a .75 mpg increase. I imagine most of this was because of the Big Ass air cleaner allowing the engine to take advantage of the cooler air. Now with that said after that test was done I started playing with the setting (this also includes putting my foot in it more often) and actually lost the .75 and even lost about .5 as well. As well as the Banks stuff works you find yourself driving the truck differently because of the additional power. I have since done some tweaking and match the original MPG but have some extra performance I did not have without the Banks stuff. As many has said the pedal monster is a must, you actually find yourself not pushing down as far (and even more then is necessary) to get the normal acceleration much like the old style cable system.
I would really love to put in the upgraded tail pipe but the dick heads at my local Chevy dealer would have a sh1t fit and give me crap. For some strange reason they think if the megaphone exhaust tip is missing they think your deleted. When they see the Data monster and super gauge they always ask if its reprogrammed, I then point to the DPF and DEF tank and the conversation usually ends.
As it is I remove the derringer and pedal monster before I take it in for service just because I don't feel like playing the game with the dealership.
Since I put in the Banks system I actually see less buildup on the MAP sensor I give it a soaking spray, let it sit and spray it again and back it goes ready for some more miles!
I really can't say enough about the Banks products, and short of a full delete its really the only way to go IMHO.