2006 Chrysler transmission problem

I have a 2006 Chrysler Sebring Convertable. I had a shutter in the transmission that I got tired of and took to a transmission shop. He rebuilt the transmission. This is a transmission place that I've gone to for several years with various cars. I trust this guy who's "never done me wrong". He's always been upfront and never taken advantage of me in any way. A year later it started to do the same thing so I took it back, the guy dropped the tranny again and he found antifreeze in the transmission. This tranny is NOT connected to the radiator for cooling. It could be some dumb ass did this on purpose but regardless of how it happened (it certainly wasn't me) I had to put in a new torque converter. The problem was solved for about a month. But then it started to hesitate when it up-shifts from 2nd to 3rd. Now I have a big "clunk" happening. It's almost like it stalls for a brief moment before it shifts and then it slams into 3rd gear. This doesn't happen when I'm accelerating at a higher RMP. It only happens when I let up on the gas after leaving a stop sign or turning a corner in city driving or when I'm accelerating slowly from a dead stop. I took it back to the transmission guy and he, without charge, dropped the transmission once more. He could not find anything wrong and reflashed the computer. It worked properly for about a month and then... once more... it's starts slamming into 3rd when accelerating slowly. It NEVER does this when accelerating quickly at a higher RPM only when I'm slowly accelerating in town at a low RPM. Any clues on what to do? :confused: