Sorry, the NHTSA has not posted this TSB document yet.
You can still get the detailed info from Chevrolet for this TSB. Call your local Chevrolet dealer's service department & ask for a copy of TSB# 010866005.
INFORMATION REGARDING NEW PICKUP BOX REINFORCEMENT KITS WHICH ARE AVAILABLE FOR CUSTOMERS WHO MAY WANT TO INSTALL A CROSS TOOLBOX, SIDE BOX, OR A LADDER RACK SYSTEM AS AN ACCESSORY. *TT