how can i tell if i have a 28 or 31 spline axle in my rear ?
someone told me if i had ABS it would mean i have a 31 spline.. is the correct ?

 

Can't help you with out counting the splines. Perhaps others will chime in and give up good info.

 

I am assuming you have a 1/2 ton with the 8.8 rear- if so you do indeed have 31 spline axles. Cars with the 8.8 such as the mustang came with 28 spline axles.
Looking at your pictures your truck looks like a 3/4 ton so I don't know if what I told you will help. Nice truck by the way.
Regards
RSH

 

its a 150 1/2 ton so i guess it is the 31