I just bought a 2001 z71 with 252,000 miles on it. I put it on a lift last night to look it over pretty good and do some lubing on it. Differential was low, but attached to the differential is a factory tag saying to use full synthetic 15w-40. I have never heard of any vehicle using that fluid for the rear end. Does this sound strange to anyone else? Does it sound right to anyone? I'm not a mechanic, but I grew up on a farm, and we had to do a lot of our own repairs, so it's not like I haven't worked on a vehicle before either. I could use some input from some people that know more about it than I do(probably most of the people on here). Please and thank you

 

yep strange indeed. what diff do you have?