Mileage Drop, MPG Gage Acting Funny

[imalabil]

Here's one for you: My 2002 3.0 mileage has dropped from about 18 to 16 MPG and the MPG gauge (vacuum gauge, I'm assuming) is acting strange. It's spending a lot of time in the low vacuum range (low MPG) even when light on the throttle. When coasting it will go to max MPG but occasionally move from the pegged position to a lower reading. I suspected a vacuum leak somewhere, especially the rubber line that goes behind the VC, but don't hear anything or feel any cuts. Also, NO SES light. It seems to run strong otherwise.
Any ideas out there?