Returned returned from a 1400 mile trip from Ohio to the Smoky Mountains etc. First trip in my 2004 Grand Marquis, car got 24.1 mpg-- that's driving about 5 mph over the speed limit with four adults and trunk full of luggage.

I just changed plugs before the trip. I was impressed with the gas mileage. BTW best gas price I found was $3.69 in Knoxville. Highest was $4.09 in Cincinnati.