Torque converter chatter?

I replaced the engine in my 95 T&C a little while back and it has developed a vibration at idle in gear. It seems to get worse as it sits idling. In other words, I can't feel it when I first stop, but as I sit like at a stop light, the vibration seems to start slightly and increase. If i put it in neutral or park, the vibration goes away. It also goes away if I pull off slowly. I can also feel it under moderate to heavy acceleration, but at cruising speed, I don't notice it. I read somewhere about "torque converter chatter". Does this sound like my problem? If so, what can I do about it? Thanx for any and all help!
Tom