I bought my 2006 WK with about the same mileage, and a supposedly rebuilt motor and fully serviced drivetrain. FWIW, since purchase last year, I replaced the engine oil with 5w-20 Mobile 1 synthetic in my 5.7L engine, and Royal Purple synthetic in my QuadaDrive II diff's. I've been told I don't need the Mopar friction modifier if I use the Royal Purple, but I did it anyway. I haven't done my tranny or transfer case yet.

My engine seems to really like the Mobile 1 compared to whatever was in there previously. No more spurious MDS related faults since I changed oil.

 

I bought my 2006 WK with about the same mileage, and a supposedly rebuilt motor and fully serviced drivetrain. FWIW, since purchase last year, I replaced the engine oil with 5w-20 Mobile 1 synthetic in my 5.7L engine, and Royal Purple synthetic in my QuadaDrive II diff's. I've been told I don't need the Mopar friction modifier if I use the Royal Purple, but I did it anyway. I haven't done my tranny or transfer case yet.

My engine seems to really like the Mobile 1 compared to whatever was in there previously. No more spurious MDS related faults since I changed oil.

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gotta love that smell of the Mopar friction modifier

 

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.

 

The only thing I have is the engine oil and coolant record plus some repairs. I think it is safe to do an all oil change. I will check with service shops on oil specs. Thanks

 

stick with mobil one synthetic and i think you will be fine.