Loud Clunking Noise

Over the past few months if not more, some days it seems worse and some times not at all I have been hearing and feeling this loud clunking noise when turning a corner or backing out of the driveway coming for the rear end. It feels like the wheels are grabing and then a clunk, kinda like the brakes are grabing. Its a pretty new Mancini Racing Centersection MRE875489 ( Mopar 489 Rearend 8 3/4 " ) 355 gear. The noise is worce when making a turn at very very low speeds, it has never made the noise from a dead stop going straight. If I roll into a turn it doesnt make that noise, but right or left turns from a stop it does. I have looked at the ujoints and all seem to be fine....
Heres another trouble, last year when i put the new motor in I needed help to turn the weels to get the drive shaft in when mounting the ujoints... meaning it took a lot of force to turn the wheels to get the ujoint to line up. You cant spin the wheels when up on jack stands like the free rolling front ones, it takes a lot of force to turn the wheels... if that makes sence. i dont have a problem removing the Centersection but just wanted to pass a few things through you guys first.....

Any thoughts ????