This product page is for tuning of GM T42 Transmission Control Modules (TCM) for use with the 4-speed 4L60E/4L65E/4L70E/4L80E electronic automatic transmissions. This service is required when using a transmission that was not mated to your engine when the engine computer was programmed. Failure to have the TCM configured at the same time as your ECM will result in inoperable conditions. It is NOT performance-based tuning although the engine and transmission can be expected to operate at higher levels due to changes in the heavy safety removed from the OEM tuning.