The 74 K10 is full time 4 wheel drive, there are no locking hubs because it is always spinning all four wheels. Hi vs Low refers to the drive ratio of the transfer case, Hi is a 1:1 ratio (for every 1 turn of the transmission output shaft, the output shafts on the transfer case make 1 turn) Low is 1.96:1. You should be mostly driving in hi. Others here will be able to explain the loc better than I could