What tranny do you have? Over all 4.56 for 35s works well for a dd. Trail rig you might want 4.88's, but again a lot depends on the tranny. Also find a shop to install the gears, that will let you see how its done, if it was easy everyone would do it. As for the detroit, it replaces your carrier so no worries there.. I however would look into a selectable locker as it will be far better, cause less wear on the axle and increase tire life.