Sounds like ATF is leaking between the cooling cores in your radiator. I have seen previous posts that have warned of transmission problems if and when the coolant leaks into the transmission. When you shut the car off, coolant pressure usually rises slightly since the heat soak begins without any air flow and there is not any transmission fluid pressure to keep the collant from entering the ATF side of the radiator. I would get a second opinion quickly.
87 300TD, 160,000 miles
72 280SEL 4.5, 250,000 miles