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# PIT-4835.
GMC/CHEVROLET: HEADLAMP SWITCH INOP IN MANUAL MODE ONLY. HEADLIGHTS ARE ALWAYS FUNCTIONAL IN AUTOMATIC MODE. THIS COULD BE THE RESULT OF A RELAY INSTALLED IN THE INCORRECT POSITION WITH THE UBEC. *PE