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# PIE-0043.
CHEVROLET:GMC: ENGINEERING INFORMATION-FUEL TANK PRESSURE SENSOR, DTCS P0446, P0451 OR P0454 SET. GMC ENGINEERING IS ATTEMPTING TO DETERMINE THE ROOT CAUSE OF THE ABOVE CONCERN. *PE