Its going to be hard to tell on fuel right now. (winter blend) Try Chevon, I believe Kroger is Shell not bad fuel, Exxon is okay but not the best mileage.
I don't know about everyone else but it only took $22 to fill up yesterday. I can care less about mileage. (smoke em if you got em) I am going to enjoy this while I can.
The auto with 3.15 gear accelerates fine at highway speeds without the need for a downshift. The Altima 3.5 has a fine engine but I do not believe car for car neither down shifting it would be faster than a 5.0. You can vary the ratio slightly but over drive is over drive. So our factors are...