This is a Rear of Rear Leaf Spring Hanger Kit it fits your:
1999-2007 GMC Sierra Classic 1500
1999-2007 Chevrolet Silverado 1500
2007-2009 GMC Sierra 1500
2007-2009 Chevrolet Silverado 1500
2007-2009 GMC Sierra Hybrid
2007-2009 Chevrolet Silverado Hybrid
This includes everything you need to mount this
Left = Right
Measures about 9"x 8"x 6"