My Pa always said you are on the right path, when you keep breaking different things (as each past break gets upgraded). He went on to say those people who don’t break parts are not pushing their cars.
One thing I noticed is there is not much (or any) grease on the U-joint needle bearing surface. I suspect the lack of grease for U-joint could be a cause of failure.
The old joint caps are missing. If U-joint got installed without the retaining clips, one (of the caps) could have worked loose and out, once an imbalance occurred under WOT the yoke gave out.
I can’t tell by the photos if the yoke is cast or forged from where the loops broke at. If a "cast part" breakage would show a coarse casting (so to speak) at the breakage.
A forged part generally show (if not beat to death) would stretch before breaking. One corner shows to be beaten to death, so that corner can’t be used to tell.
The extension housing has a couple of shiny areas at the breakage – which might mean it has been cracked for a while, possibly. Any imbalance at WOT will beak those extension housings without thinking twice about it.
If this is a 727 transmission, Dodge made a heavy duty version tail housing that helps these problems. The snap ring cover is on side of housing instead of under the transmission mount (the way to tell if you have a HD housing).
Need better pictures with better lighting, to tell you anything more.
