In my opinion. I would leave your tranny alone. Modifying a 700r4 with that many miles may lead to trouble. Stock 700s dont like some of the bolt on performance stuff. There are internal mods that also must be done to make then work rite and keep them together.
If you want to firm up the shifts a little push the adjustment button and Adjust thee slider on the TV adjustment in towards the firewall a click or two.
Definatly Change The Fluid. Clean fluid is essential for long life in a 700r4