Agreed, 15k seems way too often. IIRC my '03 Chevy dually was 100k...it wasn't even recommended to check unless there was a leak...

 

You can do UOA near 15k and find out if it will go longer. I can tell you from first hand experience that it can look and smell fine and the additives can be done. When I had my Dana 80 and towing hard, some syns wouldn't even go 12k. It was in those days that I went to syn 85w140 and the extra heavy weight literally made ALL the difference in the world. I can also tell you that if you're getting metal on the magnet you can't trust the wear metal part of the UOA. More than a TINY trace of metal on the magnet every 15k is too much. Craig

 

I have changed my like the book said at 15000 then changed it 25000 and it looked new and felt like the new i put in so i will change it at 50000 and send a sample to blackstone to have it tested. That will tell me what i need to know.

 

What is the capacity of the rear diff? This thread reminded me that my stock fluid needs removing.

Thanks,
garrett

 

I just bought the stuff to do both diffs,tranny, and t-case today. I'll be changing it all for the second time. I'm sitting at 31,000 miles. I'm also sticking with the 75-90, it doesn't specify that in the manual just because thats what they felt like typing that day.
Each to their own but I won't be skipping any service intervals. My truck costs more than my parents first home,I'll be taking good care of it!