A downhole tool includes a mandrel, a sealing element disposed around the mandrel, an upper cone disposed above the sealing element and a lower cone disposed below the sealing element, an upper slip assembly disposed above the upper cone and a lower slip assembly disposed below the sealing element, at least one lock ring configured to maintain energization of the sealing element when the downhole tool is set, and a secondary lock that couple the upper cone with the at least one lock ring. A method of increasing pack-off force of a downhole tool includes setting the downhole tool and energizing further the sealing element by applying a differential pressure to the downhole tool. A method of retrofitting a downhole tool includes providing a secondary lock disposed around a mandrel, the secondary lock including at least one arm having an axial portion extending downwardly therefrom and a threaded portion, and assembling the secondary lock to the downhole tool, the assembling including engaging the threaded portion of the secondary lock to a threaded surface of an upper cone disposed around the mandrel of the downhole tool.