In over 20 years of 90% rock crawling (mild to wild) it was rare to see or hear about premature failure of a ring & pinion. The one time I do remember witnessing a ring & pinion failure was on a Scout rock crawling in Las Cruces NM on a nasty obstacle. The rear axle shaft snapped, that caused the Detroit Locker to grenade the ring & pinion.
I have a feeling there’s a common denominator to your failures. The word “flex” comes to mind first. Is something flexing too much?
Did the 3 failures happen on the same axle housing?
There could be a quality issue with the ring & pinions?
There could be an issue with the installation?
If I were you, I’d make a phone call to Currie Enterprises. John and Ray are really nice guys - I wheeled them back in ’94 on the Dusy Ershim. I’d bet a 6-pack there is no one on the planet that knows more about axles & ring & pinions than Currie. They’ve earned their reputation since 1959.
Of Course Randy Lyman has been around since the early 80s. I'd be very interested to get an opinion from both experts.
I'm curious..... why 600 lbs. of freight?
Let us know what you find out or how your axle does in the future.