Poor Gas Mileage

Take out the 4.88 gears and the 500 lbs. of stuff out of the trunk.

Just kidding:D. You say you got it back on the road. If it set for quite a while you might check the brake system for any drag that could've developed. Tires inflated enough? Timing/advance as stated above? I agree 13 mpg with some highway included is not good.