I'm new to Ford and diesels as well, I am looking at a 04 F250 4 wheel drive crew cab with 3.73 and a 6 liter diesel. I mainly do highway driving and some towing on occasion. Most of my driving is highway, probably 90% on interstate. What kind of mileage could I expect to get out of this truck? I know you can get programmers to optimize the performance and mileage but how much can you expect it to help? Thank you for any assistance.