Went back and read the entire thread. Feeling the clunk in the steering wheel would lead me to believe that the problem is in the front end. It could be the front differential. But when the front differential goes it is usually somewhat spectacular with fluid going all over the place. Have you checked the fluid level in the front differential?
Some of the symptoms you've described could be attributed to multiple issues in both the front and rear end. I still think the transmission mount should be your primary suspect.
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