Unless it's been changed by a different chip, I believe a stocker will lock up around 45mph. It feels like another gear being engaged so you will see the rpms drop slightly. Another test is to take it up to maybe 55mph or so you're sure it's "locked" and without taking your foot off the throttle lightly press on the brake pedal, that will unlock the tc if it's locking up in the first place and you'll hear the rpm's rise.
