I'm no rear end expert but here's my $.02. First, when was the last time you added the sure grip additive to the diff.?? Second, a clunk going around corners can be worn clutches in the sure grip... due to lack of lubrication and no additive or possibly a broken spider gear.

My best guess on the heat problem is the fluid is warn out and just can't provide the lubrication needed. Not sure how much this helps though.