Rear end problems??

[Steelrat]

Took the car out for a spin today and a new issue, oh joy. When shifting the 700R4 from 3 to 2 or 2 to 1 when not under load and low speed down shifting I get a big clunk in the rear end. One time when shifting when not under load, just coasting and going 3rd to 2nd and back to 3rd a few times listening for the clunk it seemed like the rear gears would not mesh, I got a bucking clunk clunk then it went away and engaged. Also when turning ( mostly left) it feels like I am driving over a rough surface, like gravel. Trans was serviced 2 weeks ago. 100%. U joints front and back replaced 2 months ago. Rear is full of fluid. Would adding more gear additive resolve, or drain all fluid and put in new? Current fluid is a year old. Broken spider gears or worn positraction clutches? I have no experience in rear/diff work. Any advice on assessing this?

Thanks