I don't know what a bad torque converter sounds like, but just to mention one other related possibility -- read a couple of these threads about a cracked flex plate.
http://www.4x4wire.com/forums/showflat.php?Cat=&Number=1112170
http://www.4x4wire.com/forums/showflat.php?Cat=&Number=1060357
There is an inspection plate under the flexplate where you might be able to see if it's cracked. I checked mine not too long ago. You might want to briefly bump the ignition a couple times to rotate it to see more areas of the flex plate. The flexplate sounds like one of more likely components to fail and get you stranded with 4Runners, Tacomas, and T100's with high mileage on the 3.4L engine with A340F auto tranny.

Even if the flexplate isn't the problem and you really do need a new torque converter, you still need to be aware of the flexplate and possibly replace it with a new one at the same time since it's probably toward the end of its life anyway. It's not like it's easy to get access to.