what year and size is your axle? 12bolt or 10bolt.
All 10 bolts have a 30 spline pinion.
It is the carrier that you want more spline count. Only the later model 1989-1991 10 bolts got 30 spline axle.
Carrier break on a 10 bolt is 2.56 / 2.73
12bolt truck axles all have 30 spline.
Carrier break is 2.73 / 2.76 / 3.42 / 3.73