2000 Camry LE 50,000 miles, V6-Lurching trany

I've had my camry since new. 2 months ago when driving in rush hour, stop and go freeway traffic the car started kicking whenever I took my foot off the gas. Happened most often if I was accelerating and then had to lift my foot off gas to put on break. I'd get a slight bucking, and thump-thud noise. It got progressively worse and I took to the dealer. They replaced the bone joint and motor mount. I picked it up and drove it and no change to the problem. I had to drive with the technician because they were testing it in straight freeway driving and the problem was not occuring. I had them simulate stop and go traffic and then they felt it. Said it needed a new transmission. They put in a new transmission--no change to the problem. I took it back and they said it was a problem with the throttle cable. Tightened that. I drove it today and now it's worse. Not only happens when I take my foot off gas but now somtimes happens when it's shifting gears. Worse when the car is driving between 40 and 50mph.
I took it back and they say there is nothing wrong with it. HELP!
(My husband said he thought it was the U joints but the Toyota people say this car doesn't have U joints.)
Thanks