REAR END CLUNK

1998 Chevy Blazer 4x4 LS 4.3 W 150,000 miles.
I was travling around 55 mph and it felt like I hit something but I did not. As I came to my next stop I noticed a clunk sound as I accelarate or slow down like the universal joints were going bad so I replaced both of them that did not fix it so I open up the back of the transfer case and the bearing was tight and servicable. I then lifted the rear of the vehical and put it in drive the noise is coming from the rear end. It did not seem like there was alot of play in the axles and the limited slip is working correctly I am kinda lost! You can feel the clunk as you hear it. The noise is traveling into the driveshaft and thats what made me think the u joints were at fault.