Transgo THM400 TH400 400 3L80 Reprogramming Shift Kit (SK400-1&2)* FITS: THM 400 (1965-On) Installation does not require transmission removal SK400-1&2 Automatic shift. Street or full-race. Holds 1st and 2nd to any rpm. Backshifts to 2nd and 1st at any rpm. Tow & Go and Competition combination.