Ok, if the tranny won't shift right till it warms up, that leads me to believe the tranny is low on fluid. The fluid superheats and expands restoring seemingly normal function, but the transmission is actually burning up inside.

You should definately get it flushed out with the method I just outlined. Or find a shop that does it that way. Don't let them hook the machine up to it, there is a slight possibility that it could make the issue worse. I don't know what to tell you on this one, but considering the overall lack of maintenance in the transmissions history, it has likely sustained serious internal damage. My trans was run low on fluid by the previous owner, which caused me to have to pay up for a total rebuild since it scorched just about everything inside. Hopefully yours is not as bad as mine was.