1-2 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.
Operating in the downshifted position, Low & Reverse band apply fluid passes through the valve and enters the orificed PRN circuit. Orificed PRN fluid is the routed to the manual valve where the fluid exhausts.