When gas hit $4.35 a gallon some time back, I took out all excess weight from my truck (97 EB Expy 5.4L 4x4). This has the removable 3rd row seat so that came out as well. I then took off the overhead rack and removed my radio antenna (to reduce wind drag). Finally, I reduced driving speed to 60mph on the highway (from normal 70mph). Also, I frequently ensured my tires were all inflated at the correct pressure. With all these changes, the trip computer showed me at 16mpg. Nowadays, I'm getting more like 14mpg according to the TC as I'm driving at 70mph again. Roof racks, antenna and 3rd row seat are still in the garage.

HTH