there should be a sticker in the glove box that says.

 

Going from a 3.92 to a 4.1 wont yield you much difference. I would just stick with the 3.92s and get an LSD installed. I have 3.55s and wanted to get 3.92s and an LSD dropped in and it would cost me $2,000. with just getting the LSD installed only about $800. If you take your 3.92s and up them to 4.10 your only getting a .18 increase. with 3.92s to 4.56 you get a .64 increase. Obviously this means that per every rotation of the engine, thats how many more revolutions your gears would make. If you do gears and have the money to burn on it then get the 4.56s. Otherwise just stick to your 3.92s.