GM 4L30E Transmission Superior Shift Correction Kit This Shift Correction Kit from Superior will improve all 4L30E Transmissions from 1990-2005. This Shift Correction Kit corrects or prevents the following problems: Bell-housing gasket blowout, repairs case leakage in servo, weak shifts, lock-up chatter, better lube, premature clutch & band failure, and improves overall performance for regular & heavy duty applications.