You should be able to see if it is on your window sticker. most dealerships put them in the glove box
You can jack up both rear tires and spin one side forward. If the other tire spins in the same direction, you have the locker, If it goes the opposite. You have an open rear end.... ( at least this used to be how the true lockers worked)... I will bet my lunch money, it still works....
You can also look at the sticker in the bottom of your glovebox. This has all the codes for the factory installed options for your truck listed on it. You should see G80 somewhere in the list - probably near the G's
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