Low and Reverse Servo
WARNING: This page is about a different car, the 2004 Pontiac Sunfire, 2004 Chevrolet Classic, and 2004 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
Reverse fluid is routed to the outer area of the servo in order to increase the servo apply pressure in the Reverse position. The low band fluid is routed to the 3-4 shift valve. The pressure moves the 3-4 shift valve against the 1-2 signal fluid.