Are you still breaking these? Are you getting wheel hop? That is the number one killer of axles breaking, not just force on them. I have seen people just destroy axles over the years. I did the basics to stop wheel hop, like getting solid motor mounts, bushings, and suspension, and I never broke one no matter what I did. I had 0 wheel hop.
You may want to consider finding and eliminating all instances of wheel hop, if you want to stop breaking axles
Weight also helps out tons. My buddy's are running 10.7's @ 133 on stock axles and transmission, pulling 1.70's. Every pound you take out helps more and more.
--mark