Find your RPO code label and look for codes such as GT4 (3.73), GT5 (4.10), GU4 (3.08), GU5 (3.23) or GU6 (3.42). If you see "G80", then you have the OEM limited slip (Gov-Lock) differential. I don't know if there's a specific RPO code for the open diff. Also, I don't know exactly where the label would be on your Yukon. Early 2000s and older, they were in the glovebox, usually on the backside of the door. It may be on the passenger doorjamb. It's a white sticker, about 3"x2" with a bunch of 3-digit codes on it. It'll have your paint code on it as well, if that's useful to you. If you don't have the RPO sticker, you can stop by a GM dealer and give them your VIN and they can print up a build sheet for you. If they tell you they can't, find another person or dealership that knows what they're doing.