WARNING: This page is about a different car, the 2008 GMC Yukon and 2008 Chevrolet Tahoe. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Sun Gear and Sun Gear Shaft
Courtesy of GENERAL MOTORS CORP.
Callout
Component Name
1
Sun Gear Shaft Assembly - 3rd Position Tip:
You might have to rotate the shaft to align the splines.