Just curious what the best setting would be for a 700+ mile trip all open highway (I95). I drive everyday in 3 but would it be better to step down for the trip to get the best MPG???? I am not going to be towing anything but will have about 1200 lbs in the bed on the return trip.

I think you will get just as good of fuel mileage in any level as long as you keep your foot out of it.