Her car is an auto but we were considering to rent a tow dolly and I'd pull her car backwards on the dolly and she'd ride in the truck with me, but it would cost more to rent the dolly ($100 one-way) than for the gas to drive her car. Plus, the idiots at the U-Haul center where I live said I cannot tow her car with my truck because a 1/2 ton F-150 doesn't "weigh enough" to pull her 3500lb car, even though it's rated to tow 8000lbs (I got the heavy-duty tow package and the 5.4L V8 engine in my truck).
But anyway, when I mean empty, I mean she is going to drive her car EMPTY. I was going to put her trunk liner, spare tire, jack, all the stuff that she normally keeps in her car as well as unbolting the front passenger seat and putting everything in my truck. With all the stuff that we are already going to load, I estimate that I'll get 10-12MPG on the freeway, while she could easily get 30+ MPG drafting behind me. Her 'Stang is a V6 by the way.
Anyway, thanks for the suggestions...I'll report back after the move with the MPG numbers.