Sonnax HD 2-3 Shift Valve 4L60-E Sonnax has developed a drop-in replacement 2-3 shift valve that applies the overrun clutch in D3, 1st, 2nd and 3rd gears where the factory valve applies the overrun clutch only in D3, 3rd gear.Applying the overrun clutch in 1st and 2nd provides added durability to the input sprag and forward clutch in heavy duty vehicles, plow trucks and high performance applications.In addition, this upgrade works well with applications using aftermarket electronic paddle shifters. With the overrun... No special tools... Extends life of the forward clutch and input... Ideal for electrically downshifted units with aftermarket paddle...