SebringLTD

I have a 2004 Sebring LTD convertible with the 2.7v6 and 4-speed automatic. 480,000 miles.
In December we had the transmission flushed as normal maintenance. In January it was very cold, well below zero, and with a cold enginer the transimission was occasionally clunking. Two weeks ago the dealer checked, confirmed the clunk, and said the fluid was low, their fault as they did the flush, and topped it off at no charge. Two days ago it was around 10-15degF and it did it again. But it won't do it for the dealer and they say everything is fine. Explaining to them that it's the exact same issue that they confirmed two weeks ago gets no results. They don't know what to do. Any ideas or suggestions? Thanks.

SebringLTD

Correction. Just 48,000 miles. Any idea what may be causing the clunk? Or how to get the dealer to respond to the issue? Thanks.