2002 GMC Safari TRANS LEAK

Hello. I have a 2002 GMC Safari 4.3 V6 with a 4 speed 460LE trans w/tow haul mode. The van has approx 80K miles on it. The trans has developed a significant leak just in the last week or so especially at highway speeds and when downshiting. The leaking fluid is spilling onto the exhaust and causing a fair amount of smoke. I have changed the fluid and fiter 3 times in the 4 years I have owned it (every 15K). The leak is definately coming from within the bell housing, not the pan. I realize that I will have to remove the trans to repair this leak, but was hoping for some insight as to what may be leaking. Could it be something as simple as the tourque converter seal? Where else could the fluid be comming from?