I bought myself a new car this year and of course, my wife took it and gave me hers. I had noticed when I changed the oil or moved her car over the years that she averaged about 33 MPH and 19 MPG. Now that I drive it, I also average about 33 MPH but I get 23 MPG on the average. Every time I have to follow her somewhere, I give up trying to keep up. You are right that driving style makes a big difference. I get a lot more miles out of my brakes than she does too. No surprise.
As the the 2.7 or 3.5 Eco. I had decided when I get around to buying a new pickup it was going to be the 3.5 Eco. I am not sure now. I like the 2.7's CGI block and to want see more data.