Doug,
I broke a 31 spline Yukon axle this June at the all ford race in Kentucky that I go to every year, the axles are well used and well over ten years old, last 6-7 have been taking the abuse of the wide open transbrake launches and mid/upper 1.5 60 foots at 4000 lbs, they are/were on borrowed time, they are also in the older, lighter housing, not the heavy truck housing that most people use. Anyway I don't trust them anymore, they been good to me for a long time, just time to upgrade for reliability sake, and to ease my mind, the suspension has to change because the new housing/ axles are 4 inches narrower than stock, the tires/rims would rub on the springs if I didn't relocate the springs closer to the frame, I went with the narrower housing to help tuck the tires inside the fenders because they stuck out of the fenders and I didn't like the look, the upgrade to rear disk brakes will be a welcomed improvement also, heavy object moving fast is hard to stop quickly lol. Anyway, just like every other project of mine, they snowball out of control really fast.