3-4 Shift Valve
WARNING: This page is about a different car, the 2009 Cadillac DTS. However, it is still accessible from the selected car via links, so may be relevant.
Spring force and D321 fluid hold the 3-4 shift valve in the downshifted position. Fourth band fluid from the 1-2 shift valve is routed through the valve into the orificed D21Y fluid passage. Orificed D21Y fluid is then routed through the 2-3 shift valve, where the fluid exhausts.