I have a 98 Windstar with the 3.8 (no antifreeze in the crankcase, thank
goodness!) and 94K miles.  The gas mileage has taken a nosedive of late -
overall mixed driving is returning less than 14 mpg.  EPA estimates are 17 &
24 for this vehicle, and that's about what it used to get.

I just replace all six spark plugs & wires hoping that would help - put in
OEM Motorcraft plugs, AZ wires - since it had been running less than smooth.
It purrs like a kitten now, but mileage has not improved.  I know that
swapping plugs was a long shot, but figured it wouldn't hurt.  My wife
normally drives this, and I'm not sure how lead-footed she is.  The tire
pressure is good and I replaced that original steel wheels with aluminum
last summer and I think they are lighter, though I may be mistaken.
Otherwise, what else should I look for?

Thanks

G