Now we are getting into the differences between axle shafts.
The problem with these discussions is that there is no real level playing field.
A GM 60 is 30 spline, same as a LC. The shafts are different in design than the LC shafts. But they are heat treated differently as well. So they break about as easily even thought hte shaft is a slightly better design. (taper).
The PP shafts are a better material, and a better design than the LC stuff. But, since you are dealing with a relativly heavy rig and still have the 30 spline limitations they will break.
Aftermarket shafts may start out as a blank (same radius all the way to the end) and then have the spline cut into the shaft. Not a great design. You can easily cut through the hardened exterior of the shaft and create an axle that may indeed be weaker than a stock shaft.
Rolled splines typically have a root diameter of the splines that is about the same diameter as the narrowest portion of the axle shaft. Look at a stock front shaft (seal portion excluded).
So much goes into what makes an axle shaft "strong" it is silly.
Neat topic tho..
We need pics and an engineer
