I have been using the Bully Dog Triple Dog on my 5. 9 for about 4 years now. I think it is great, made the truck run much smoother with noticeable power gains. Easily installed and removed by plugging into the OBD port, can also change power modes with it. I did not gain any noticeable mileage improvement, but with the increased power I did not lose any mpg either.
I think Bully Dog does a lot of research and puts out a fine product. When I had questions, their tech people seemed very knowledgeable and helpful. Check their website for a dealer near you that can give you the "try before you buy" temporary upload. I think you will be very impressed. Let us know what you do and how it goes.