Vehicles with GM 6L45, 6L50, 6L80 and 6L90 transmissions may have complaints of vibration, shudder or roughness, particularly while driving at low speeds with a steady throttle on a level road. This complaint may be more noticeable when driving up an incline. These symptoms can be caused by a broken TCC regulator valve spring in the lower valve body, which causes the TCC slip speed to drop to zero.

With a capable scan tool, monitor the TCC slip during steady throttle input. If the TCC slip remains a constant zero RPM during the shudder or vibration, check the lower valve body for a broken TCC regulator valve spring and replace as needed with Sonnax TCC regulator valve spring 104740-45K.