I only had one bolt acturally break. The other bolts were bent and would have eventually broken.
The key here is to take all the slack out of the connection between the round shafts and the square tubes. Using the 1 3/4 inch long bolts also helps, because the threaded area of the bolt is no longer in the stress area.
My factory supplied bolt that broke was a grade 8, so grade 8 bolts by themselves are not a fix.
What year is your trailer? The slide mech was changed to a completely different vendor (dexter) sometime in the 2008 model year.
I also found that the in stops for my slide were not adjusted correctly, this caused the end seals on the slide to be overly crushed toward the bottom of the slide. I don't know how much this had to do with the bolt shearing issue, but M-Tec, the slide mech manufacturer says to check it relative to this problem.
2007 Rockwood 8315SS
2014 Silverado 2500HD 6.0L