Just passed 1600. I figured it would get a little better with time, but not expecting much more than what I've got, without driving 60 all the time.
I live in the hot n humid south too. I drive to Charleston, SC alot too which is about 300 miles and I avg 44 mpg doing 70 - 75 mph. Im assuming you have the auto AC? After driving for 10 mins put the fan bars at 2 only and cruise, not full blast (over 4 fan gauge bars) and you'll squeeze out 40 mph I promise you. The volume area cools pretty fast so full blast all the time isnt really needed. Im constantly overriding the auto AC and dropping the fan gauge bars to 2. Keeps me plenty cool.