I have a GMC Sierra, 2011 5.3L vehicle... This item roughly increased my MPG from 17 to 19.5 for both highway and city use. Now I was really concervative with my driving, if your punching the gas pedal your not going to get close to that. The system did change the shifting of my vehicle, I notice an improvement of shifting and responsiveness, the only problem I had with this was a faulty cable upon purchase. I called and a replacement was sent to me automatically free of charge! Good service!
The bullydog has not lived up to any hopes for me to improve mpg. But first of all, the package says you can change on the fly. Well you cannot and it takes 7 minutes to delete or add a program. So if you want to experiment, it takes 14 minutes to change to a different program. Secondly, the unit is so small that it is a struggle to read the info. Lastly, there was absolutly no change in mpg, there was more pep for sure, but that is not what I was looking for. I will be returning this unit.