Yes, it's all one piece. The bed pans bolt to it, and the rear valance panel goes behind the bumper, where the splash shield screws into that part.
The LMC part number, out of the CSB.13 Catolog, is 38-7989. Their price is $139.95, plus shipping. The GM part number is 15606605. The price from gmpartsdirect.com was $166.05, plus shipping. I bought the GM part in October and paid $36.35 for S&H.