Loud thunk at idle after coming to a stop

[GMblood]

Driveshaft support bearing and the 3 u-joints were replaced but vibration still continues. Could just be the tires out of balance or something after all, but either way ill take the new parts. As far as the thump goes, after driving it again and really paying attention, it doesnt just happen when i stop or have my foot on the brake. So I dont think anything is binding. The mechanic said that it could be the torque converter clutches which i would have to agree with. Im going to check the tranny mount and the torque converter/flexplate bolts along with putting some additive in there and see if that helps. Maybe change the filter and drain some (not all) fluid and refill in intervals to eventually have fresh fluid rather than a full drain and fill which ive heard can be catastrophic.