So I lifted my jeep with 2.5in foa coil overs in the front and a block lift in the back. I have 33 in tires on it currently. It is a 91 Cherokee briarwood. I was test driving it on a dirt trail in 4wd part time. I began to put it back into 2wd and there was this awful grinding sound. I looked under my car and my drive shaft had come out of the rear u joint and the seal cracked. I replaced the seal and the u joint and test drove it In 2wd and within 5-10 minutes the same thing happened. Idk how to repair it now with our it breaking again.



I took this seconds after it happened

 

Those are some tall blocks and it looks like your leaf packs are pretty soft. I wonder if the axle is wrapping and causing an impossible angle for the driveshaft to support, thus it's popping out and spitting caps. Did it happen just coasting along or when you were on the throttle? Flat ground or bumpy? And it looks like your pinion angle is really pointing high. How much lift, and any axle shims?

 

I was stopped on dirt at the time

 

your yoke ears might be stretched ,I would try a junk yard drive shaft