Might be transfer case if its 4 wheel drive. Have a 2001 pickup that would not move and it was transfer case. No
oil in case. The
oil pump wears a hole in the case and you lose all
oil. Common problem with G.M. The fix is a new case with stainless wear plate at oil pump. The hole will be at the bottom rear of case. 2001 pickup is company truck driven by employee, you would think they would see oil on driveway or back of truck? Have a 2006 pickup that I drive so first thing I did was check it out. The local G.M. dealer said the problem was addressed in later trucks, case has stainless wear plate .