I believe that 3. 73's are standard and 4. 10's an option. If he looks in the glove box, on the back surface of the door, there is a sticker that shows options and such. I know that it shows the 4. 10's on mine (option) though I don't know if it shows when you have the 3. 73's... . It might just show options.
What RPM is he turning ?... at 60 I am at about 2075 with the 4. 10's