Well after 3 tanks the vacuum gauge has net me an extra 1.5MPG average. I went ahead and ordered a MPGuino from JellyBeanDriver. I have the ability to datalog right now but there isn't any real time easy numbers I can look at for efficiency other than the injector pulse width.
Something else I did was to install a brake light button for 2 reasons... 1 people here get right on your ass and don't pass you. I can hit that button a few times to act like I'm slowing down so they get in the left or center lane. The other reason is engine braking. People in their automatics don't know what that means and plow in to the back of you. When I exit the freeway I can engage DFCO and push that brake light button.
Here it is...
When the brake lever is down I just rest my hand on the hand brake and push the button.