What is the best speed (mph) to drive on the highway if I want to conserve gasoline-i a drive 95 chevy lumina?

Mathematically, the best speed to go to conserve the most fuel is 55 mph. If you were to go 60 - 65, you'll be ok and save lots of frustration from other motorists. From there fuel consumption increases exponentially because the increase in wind resistance at the higher speeds makes the engine work harder. Below that you burn more fuel because it takes you so long to get there. Also, fuel conservation is best when cruise control is used because the engine maintains a constant rpm.