Lo & Reverse Clutch
WARNING: This page is about a different car, the 2008 Isuzu Ascender, 2008 GMC Envoy, and 2008 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
As in Park, PR fluid pressure acts on the outer area of the lo and reverse clutch piston to apply the lo and reverse clutch. Also, Lo/reverse fluid from the lo overrun valve acts on the inner area of the piston to increase the holding capacity of the clutch (see Note below).