I have a 2000 Bravada that has the "hopping" problem during slow speed turns such as parking lots, etc. The transfer case fluid has beenchanged twice in 2.5 years, the last time being a year ago using the recommended GM fluid. The hopping has gotten worse and a GM dealer told me since I have a locking differential that I should probably change the rear differential oil as well. The owners manual says to only use GM axle lubricant, PN.1052271. There is no description of what that lubricant is. They also give the same part number for the front axle lubricant which is a standard differential and call it "SAE 80W90 ". When I called the dealer they tell me that my book is wrong and that I need this special SAE 75W90 oil at about 29.00 a quart. Now if someone could please answer six questions for me /i would be extremely grateful: 1. What is the correct oil for this axle? 2. How much do I need for a complete drain and refill? 3. Is there a drain plug on these axles or is there a plate on the rear of the carrier that has to come off? 4. How likely is it that a rear differential oil change may cure my problem ? 5. If this is my problem what is actually happening in the differential to cause this? 6. How much damage typically occurs from driving a car with this type of symptom for any length of time and what will we notice? Thanks very much for any advice. Lenny Stein.