As dvdswan said the ONLY GM truck to have anything other than an open differential was a few military 5/4 ton trucks. Those were identical as the M-1008 but were designated M-1028.
The M-1028 had a Dana Trac-lok in their Dana60 front axle. The Trak-lok is not a locker, but a single clutch cousin of the two clutch Dana Power-lok.