#23X. Fits 4R100 transmissions. Converts long slow soft torque converter lock-up to a short crisp ON / OFF lock-up. This kit is an add-on to a Transgo Shift Kit or Reprogramming Kit, which increases lube flow and furnishes additional pressure for lock-up. We don’t recommend installation of this kit as a stand alone add-on. Transgo #4R100-LU.