According to the previous owner of my car, there is a 3.91 diff installed in my 530.

I really liked it in the beginning, but now since I am travelling more on highways, having the tach at 4,000 all the time is a bit distracting. How would I go about finding another one, or trading it for another? Anyone interested?

Isn't the stock diff 3.15 or something around there?

Thanks