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If you want to find a 4L60E in the wrecking yard and upgrade it to 4L65E specs, find one that was built after 1995, when GM converted the 4L60E converter lockup circuit to a pulse-width-modulated circuit. This type of lockup circuit offers a smoother transition, as it pulses the signal instead of jolting the driver with a sudden converter lock. These transmissions will be marked with "PWM" on the front of the pump. The important thing to remember here is that whatever the type, PWM or non-PWM, it must match the computer in the car; otherwise it will not function properly.