GM 4T65-E transmissions often suffer converter failure during high line pressure conditions such as max adapts or various codes due to excess apply pressure. The torque converter piston is designed for operating pressures of 135 psi, but the OE apply pressure relief doesn't crack until 175 psi and can allow apply pressure to increase beyond that to over 225 psi. At these high pressures, the piston deflects, destroying the piston and lining.

Sonnax TCC apply relief valve 84757-01K is calibrated to crack at 135 psi to prevent excess apply pressure. The original cover chain can be used with this valve.