My preference is L/S over E-locker. 3.55 ratio is a good overall ratio and the fuel mileage won't be drastically worse than with a 3.31 ratio. This should be especially true with the 6 speed tranny and the 2 OD ratios. But tires will make the most impact on how a truck performs in snow and ice conditions. With the correct tire choice any option Ford offers will work out ok.