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.
High fluid pressure in the 1-2 SS valve moves the 3-4 shift valve to the upshifted position. The 3-4 shift valve allows orificed third clutch fluid to enter the fourth band feed passage. Fourth band feed is then routed to the 1-2 shift valve.