Mine broke with stock steering and 42's. It was obviously weakened in some way/fatigued/cracked before it broke.
I had driven up a fairly nasty hill in August of 2005. The hill is nicknamed "Butttpucker." It was dry, and I made it without any real trouble. When I made it over the top, I was "wiggling around" to park out of the way for the next rig to attempt the hill. The steering went limp (on flat ground), and yes indeedy....it was not fun getting it off the trail.
I considered swapping to a Chevy knuckle, as they are noted to be beefier than the Ford D60 knuckles...but nowhere near the strength of an aftermarket Dedenbear unit. I bought Dedenbear knuckles for both sides. Believe me, I was not happy with spending close to $600 on two chunks of steel that did not make the truck any more capable on the trail (IE: larger tires, better gears, locker, etc). Looking back however, I'm glad I bought the Dedenbear knuckles. My motto has always been: "If it breaks, upgrade it." I don't exactly have $$ falling out of my arsehole, and understand that this is not always possible....but almost everything on my truck that is upgraded over stock was due to need...parts were getting worn, were about to fail, I knew that I would be adding more stress in the future (planning on jumping from 38's to 42's two years ago), etc... or parts outright failed.
My advice: Due to the seriousness of the knuckle failure on the trail "PITA factor," I'd recommend carrying spares...or better yet buy Dedenbear knuckles. Like most things vehicle related, they are cheaper for Chevy's than they are for Ford's.
Roy