Look at the axle cover in the middle of the rear axle...that will tell you what you're working with...also, and i'm unsure about this, but you might be able to check the door jam sticker for that info...
that being said, it's likely a 3.23 gear ratio (maybe even a 3.53)...however if you're planning on doing any upgrading to the gears go with the FRPP4.10s; they're a sure thing
....whatever you do, don't go with anything lower, you will most likely not be pleased with anything less..fire it up