It's definitely possible I did something, but I'll be damned if I know exactly what it was. About 6 weeks ago I was on some flat straight trails and possible going faster than I should have been... That being said I haven't been on a trail in about two weeks so whatever was the final blow that caused one or both to finally give was from driving around town.

I agree the bushings seem to be the only area of difference from stock. I use the Stongflex polyurethane bushings that Sonoran Steel recommends. I'll be receiving the new arms Wednesday and I'll get some photos and see how tight they are. The additional concern this now brings up is that the same bushings are on my lower control arms

I agree the bushings seem to be the only difference from OEM. I'll investigate and report back

Can't imagine the bushings you used had anything to do with your failure. Those bushings are designed to allow rotation type movement whereas the stock bushings are clamped solidly in place and movement is by torsionally twisting the rubber inside the steel bushing cup.
How did you remove your old bushings? Did you use heat in your removal process? If so, you could have used too much and caused metallurgical damage to the arms since the picture shows the failure appears to be at the weld.
Just a thought.
I bought some new OEM style upper arms for my '03 and cut the bushings out and installed Super Pro bushings, so I didn't use any heat.
So far so good, but I don't off road.

Rockauto
Mevotech
$36 each.

Arms were thicker than oem on the set i installed on my 4th gen.
Couple years, no issues.

I think you're onto something here. I didn't do the bushings myself, I had a shop do them. I seem to remember they had a hard time getting the old ones out. I don't remember if they said they used heat or not but it seems likely. It was about three years ago so it's a bit fuzzy

Holy hell. I'm gonna have to go crawl under my truck and look at mine now lol

You got any pictures of the other side showing where the weld broke off?

Given all the mods to the truck, my guess is you have way more articulation than stock thus the trailing arms can be operated well outside of their design limitations. From looks of it, they twisted too far and simply snapped.

I'll get some better pics as I go through the replacement process

This is very possibly it. The only thing I find odd is that it hasn't happened to anyone else? I don't think my truck had better articulation than others?

I've seen bolts back out but never the upper rear control arm shear. My only assumption would be that it was somehow damaged during removal of stock bushings and/or installation of new bushings...or maybe a weird combination of things previously listed

Yeah don't drive it like that at all. The only thing keeping your axle attached to your vehicle is your driveshaft at this point, hence the shuddering.

Once the driveshaft snaps you'll lose shock shafts, sway bar mounts, panhard bar, the entire axle housing... I've seen it happen to a 3rd gen on a trail, he posted on here years ago.

Thanks for confirming. I'm not driving it now until I get it repaired. Hopefully the 10 miles I drove it didn't do any damage

while those bushings probably allow for pretty drama free rotational movement (unless their bolt got REALLY torqued down tight), i wouldn't be surprised if those links sheared from binding in axial rotation (think of articulation, one wheel stuffed and the other at full droop). without a certain degree of give the only thing left to twist is the metal shaft itself.

i don't know the durometer of these bushings compared to other aftermarket choices, but its a problem that can rear its head in other applications, such as sports cars, where stock bushings with engineered-in-compliance are replaced with performance bushings that are too stiff, which then cause bind which gets worse the further through the travel range the suspension cycles.

really glad it failed in a mostly drama free fashion for you....that could have been a Code Brown for sure.

Great Post

Poly bushings are primarily for single axis use only.
Often the poly itself will split and crumble.
When more axis are involved a heim type joint is much better choice for a performance mod.