Congratulations on your new car. I hope that you drive and enjoy it for as long as you want.
A question: If the Marquis was on the lot the next day, did you find out what the problem was that was so quickly fixed? Fuel pump or something?
Last weekend I had to travel 940 something miles round trip to an 80th birthday in Tennessee, down on Thursday and back on Sunday. My 4 cylinder Solara which normally gets 20 MPG on regular grade gasoline around town achieved 37 MPG on both legs of the journey doing between 65 and 75 MPH. I have not made a long trip since late 2000 and had forgotten how well she performs on the highway.