So today this happened.
Sheared leaf spring pins. Destroyed drive shaft. Bent rear end yoke. And cracked transmission. Punctured fuel tank. Rear end has fallen out of of cradle.
Hint it's not supposed to be laying frame.
Edit. Also it's a carbed 350 and th350 transmission

 

to bad, nice truck

so they changed the normall location to lower the spring and the new pin didn't like it?

 

It used stock pin location in the leaf spring. However it was replaced at time of doing flip kit. However the mounting place for the rear end has the locating hole moved about 3/4 of a inch to make the drive shaft long enough and to correct the drive line angle. However it still needed to have angle shims to set it properly. I'm still not sure what exactly happened. The rear ujoint actually ripped the straps through the bolt holes. The front Bent the output shaft of the transmission and cracked the case. And some how the rear end came out of the ubolts and mounting plates. Truck fell on the leaf Springs and frame so I'm not really sure what went bad first. Was only doing around 15mph when it happened thankfully.