GM 4T65-E Transmission Sonnax Oversized TCC Apply Valve Kit Symptoms: Code 741 Converter shudder Falls out of lockup when hot High TCC slip RPM No lockup Cause: Continuous oscillation of the converter apply valve in the cast-aluminum bore causes bore wear that prevents the valve from stroking to the lock-up position. Correction: Correct TCC concerns and salvage the valve body core by reaming the worn bore and installing Sonnax oversized TCC apply valve kit. Some E4OD, 4R100 transmissions have soft 1-2 or 2-3 shifts, intermittent harsh shifts or poor line rise complaints. These can be caused by ECU (electronic control unit) or accumulator pressure problems. Severe wear of the line pressure modulator sleeve allows EPC (electronic pressure control) oil to leak past the valve and cause soft shifts. Severe wear can also cause the valve to stick or hang up, causing harsh shifts. Sonnax offers four size variations of the line pressure modulator sleeve and valve kit that eliminate this oil loss problem. Sleeve is manufactured from carbon steel to prevent excessive wear. Valve is made from hardened alloy steel for better wear resistance. O-ring helps prevent EPC oil loss. Annular grooves center valve in sleeve and eliminate sideloading. Improves shift firmness.