Differential swap... rebuild time?

[TwoFiftyShifter]

I had blown my G80 10 bolt into pieces on my 84 K10, so I pulled it off. I was given a 10 bolt of the same ratio for free from my buddy, came from a running driving C10 although he never drove it, just stripped it for parts. The ring and pinion looked great, this one is an open rear.

I installed the rear over the winter and finally got to drive it this weekend. Uh... Something isn't right, not sure what though. This diff clunks loud when rolling on or rolling off the throttle. It almost can't be avoided and obviously is worst in 1st/2nd gear.

What should I look at for diagnosis? Should I rebuild the rear diff?