It depends on which transmission you have and what your tire size is. Should be either the 21 or 23 tooth depending on the above options. Probably 23 though.
Some people with 4.10's have trouble getting the 23 tooth gear to last. If you have this difficulty, you can get around it by changing the drive gear on the tranny tailshaft. Reducing the number of teeth on the tranny tailshaft will allow you to run a driven gear smaller than 23. However, you'll probably have to pull the tranny to swap that gear. I've done it twice on mine; not difficult, but time consuming.