I've been meaning to follow up and THANK YOU!! for your advice last week with my Tremec (TKO600) issue (stuck in gear).
I did what you said and removed the reverse switch. I was able to see the 'lever' inside , not really sure what position is was supposed to be in, however did see that it clearly moved with shifting from Reverse to 5th. Also since the trans seemed to shift fine from 3rd - 4th, I focused on the 1st - 2nd shifting. Slowly shifting in 1- 2, etc. then eventually (with car on lift) gave the rear tire a good budge, ...and bingo if freed up!! Now able to go through the gears and hit neutral just fine.
THANK YOU again for the help. You saved me from having to drop the trans out of the car... : )