Mid 2010-earlier GM 6L45/50/80/90 transmissions have a tendency to set a P0751 (shift solenoid 1 malfunction) code. One of the causes of this is the OE spring force at the clutch select valves inhibiting movement of the valves, affecting proper control of clutch apply fluid.
Early-model production has updates made to reduce the spring force. However the updated springs are not available separately from OE, only as part of a new and expensive lower valve body.
Sonnax clutch select valve spring kit 104740-02K updates these springs to the correct lower load to prevent the P0751 code.

No special tools required
Avoids expensive lower valve body replacement