3-4 Shift Valve (362)
WARNING: This page is about a different car, the 2008 Buick LaCrosse and 2008 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
When 1-2, 3-4 signal fluid shifts the 3-4 shift valve against spring force, it allows 3rd fluid to enter the 4th clutch fluid passage. 4th clutch fluid is forced through a feed orifice before stroking the 3-4 accumulator piston (428) and applying the fourth clutch.