Frank,
Man, I thought these Tremecs were bulletproof! I agree with Agro, it really does sound like the synchro is worn out. That is a big job, too. The whole transmission has to come apart. If you can't do the next event the way it is, better cancel. It usually takes me a day to get the trans out, a day to take it apart (very carefully, noting everything), a few days to find the parts, a day to put it together and a day to install it. And I only get to work on it on the weekend.
Have you drained the
oil and checked for pieces?
Good luck,
Paul