Greg,
Some good points have been brought up, like Foggy's example of just plain asking to much of it. I've never experienced cap failure, always teeth, but I did some things this last time around that so far seem to be working. personally, I think the #1 reason for failure in a car that is not OVER powered for an 8 3/4 is incorrect set up, by that I mean, as someone pointed out, with one exception, there are no "good" gears available for them, so we get steel gears and set them up to the manufacturer's specs...WHICH WONT WORK for very long. Those specs are for a stock, daily driver, not a race car. Every set I've ruined were set up stock, and had tooth failure because under load you can see that the wear pattern ran right off the edge of the teeth, eventually breaking them off.
Heres what I did, First: had a new set of gears shot peened for added strength (forgiveness), Second, deberred the interior of the case where the bearings & caps go to get correct tork, Third, corrected the bore alignment...it was way off, Fourth, Installed main stud in place of bolts and shot peened the caps, Fifth, set up the gears favoring the toe about 5 thou more than they called for. Now its got a good pattern on it even with the stroker motor and has about 150 runs with all its teeth where they belong. You can check the numbers in my sig. Has all this been the key? Dont know, but its finally living.