GM Turbo Hydro 250, 250C, 350 & 350C Superior Transmission Shift Correction Kit This Shift Correction Kit from Superior will improve Regular, Heavy Duty, Trailer Towing and Taxi transmissions from 1970-On for the GM 250, 250C, 350 & 350C. This kit can also be used to convert the 350C (lock-up) transmission back to the 350 (nonlock-up) transmission. This Shift Correction Kit helps eliminate the following problems: Erratic passing gear shifts, premature clutch failure, premature band failure, erratic shift points, weak shifts and will convert a 350C to a 350. This Shift Correction Kit will come with installation directions in English and Spanish, illustrations and the drill bits that the installation will require.