The rear Pumpkin should have a sticker from factory. But if someone put an aftermarket one in the past I don't know how to say other than doing the math and seen what Rpm u have at 60

 

Jack the rear end up. Mark the bottom of the wheel and drive shaft. Turn the wheel one revolution while counting how many times the ds turns.

3.73 is three and three quarters.
3.31 is three and a quarter.
4.10 is four turns.
3.55 is three and a half turns.

 

The best thing to do is to crack open the rear diff and see what number is on the gear.

 

That's an expensive option just to find out what gears in it.

 

You can check the codes on your door...there should be a sticker inside the outside jam.

Here's the codes

8 = 2.73:1 w/ non-locking (open) differential
M = 2.73:1 w/ locking (Traction-Lok) differential

Y = 3.08:1 w/ non-locking (open) differential
Z = 3.08:1 w/ locking (Traction-Lok) differential

5 = 3.27:1 w/ non-locking (open) differential
E = 3.27:1 w/ locking (Traction-Lok) differential

F = 3.45:1 w/ non-locking (open) differential
R = 3.45:1 w/ locking (Traction-Lok) differential

6 = 3.73:1 w/ non-locking (open) differential
W = 3.73:1 w/ locking (Traction-Lok) differential

 

LOL those look like fox body gears.

 

Cliffy k did a calculator that is pretty dead on. If u search it's in one of the threads.