[baumbr]

I presume that you do not have a check engine light shining at you, or perhaps the bulb is burned out or missing (like on my '92 when I bought it). Did you do wires, cap and rotor while you were doing the plugs?

Check your emission controls and sensors, as well as all vacuum lines. Any of these will throw off your mileage, and may not cause the CEL to come on.

Are you driving with the hubs dialed in? The increased drag from the front axle will reduce gas mileage as well.

Good luck and keep us up to date.