Ive got a 03 Edge and mine does the same thing but its not a huge difference. This truck is about 2 inches higher in the rear also. Mine isnt always as dramatic as 1/8th of a tank but it is clearly noticable. I just always assumed that its normal because it is lower in the front.
2003 Ford Ranger Edge 3.0L Vulcan Auto Tranny
MAC Performance Ram Air Intake
Flowmaster Super 44 w/ tailpipe before the wheel
Interior and Exterior LED w/ music interface
Ford Racing front and rear Sway Bars
Limited Slip with 4.10 gears