I take it you have the 4x4?
I ordered one of the most fuel efficient configurations outside of the HFE versions. 4x2 3.21, so I'm hoping I can max that out. I also cruise a lot at around 71-72 on the highway, trying to go a little faster than the big rigs, but not killing my mpg. I'm hoping to get at least the EPA rating on my long trips. Hard to say what my mixed driving will do, I have a bit of a heavy foot, but my Frontier is only getting about 17mpg on average.
I'm hoping the savings will come as prices come down, but I'm more concerned about the value of my time, and again, having a large tank buys me more patience and patience usually pays back when I have time to shop for good prices and cash-back.
The bottom line is that I need a truck, no matter how you cut it. I cross-shopped truck-based SUVs and pickups to get good interior space, comfort, and towing capacity. Nothing else in this segment can beat the EcoDiesel, even if Diesel prices are high. Pickup trucks aren't exactly going to blow anyone's mind with MPGs, but I'm maximizing on what I have to work with, plus I amaze people when I say that my new pickup truck will get 32/33mpg on the highway.