What's up with that sidewall? Maybe a belt twisted or something? The cracking wouldn't make me nervous, but the sidewall shift does. Good idea on the new tires.
A few posts up you mentioned the mileage. 12-13 seems pretty normal for these trucks unloaded. My 2012 with 3.73 gears would only break 13 mpg on easy country roads, unloaded, cruising at 50ish in mild spring or fall weather. Any change to that exact condition would drop the mileage.