I'm more interested in the 15.6 mod for ease of filling to the total capacity. I have an hour+ commute to work, I don't have the extra 20 mins (I'm guessing here) to trickle fill the last several gallons. Also, not too keen on always needing to have fuel in a can at home to top off without a shutoff.You can get 700+ miles without changing out the fuel pump. I'm convinced GM underrated the ECO MT for fuel economy. I haven't touched the fuel pump and have 715 and 814 mile tanks. I normally run 350-400 (winter) and 475-525 (summer) between fill ups.