Torque Converter?

[ticopowell]

That makes sense, I knew about the "fans" inside the AT, so the torque converter basically locks the engine to the tranny. but why then does it only lock when I am going at a steady speed? if I floor it at 65 with it locked, it unlocks as the truck shifts to 3rd, or 2nd(forgot which), then it doesnt lock up again until I am cruising again... that normal?
oh and thanks for the quick reply!