[dmsfun]

Did you get any maintenance records ? Trans fluid is 100k interval, diff's are 30k, etc.. It is costly to have these fluids changed out, and it is a waste of money if it was performed and not needed. FWIW, I do not recommend Royal purple products, tried their engine oil and it ran the roughest of any oil, particularly in MDS as if it is too viscous.
Amsoil is far better for engine oil aas uiut runs a lot smoother, and their diff fluid is top of the line and does not require friction modifier. There is a comparison chart of all available diff fluiids and their test results on Amsoil's site.