The 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.
This valve operates in the downshifted position. The valve allows orificed PRN fluid to enter the Low & Reverse band apply fluid passage. Low & Reverse band apply fluid is then routed to checkball #6.