[MetroMPG]

Just had a thought: if you're interested in tinkering, you could probably do this for free with a little investigating.

Your vehicle already has an electronic vacuum sensor. If you can locate it and tap into it with a digital (or analog) voltmeter, you could use that info.

The goal under cruising/accel (with most auto transmissions) is to keep whatever reading corresponds to the highest vacuum (lowest manifold pressure).