Differential locking systems for a surgical instrument that includes a surgical end effector that is powered by a rotary drive shaft assembly that is movable between a plurality of discrete axial positions. In various forms, at least one retention formation is provided on the rotary drive shaft assembly that corresponds to each one of the discrete axial position. At least one lock member is operably supported relative to rotary drive shaft assembly for retaining engagement with the at least one of the retention formations when the rotary drive shaft assembly is moved to the discrete axial positions associated therewith.