Lost every Sierra key?
No key left for a 2007 to 2013 Sierra usually means GM's relearn: with the fresh key turned to on, the security light stays lit for around ten minutes, then off, three times over. Cutting the blade from the VIN code comes first, and the timers add about half an hour on top. Newer Sierras learn keys through the OBD port, where GM's security timer can still add a wait.
A lost-key job adds $60 to whichever key the truck needs: $125 plus $60 for a 2016 Sierra, $229 plus $60 for a push-start 2022. Bring a license bearing the owner's name and the title or registration. The truck never leaves the yard, and the key that went missing gets locked out of the Sierra at no extra cost.