2004 Stratus Transmission slipping

My wife has a 2004 Dodge Stratus 4 cylinder automatic car. We had to replace the transmission 3 years ago because it kept slipping during the winter months which resulted in the gears being stripped. After we replaced it it ran fine for 2 years and now in the 3rd year of the new trans it is starting to slip again when it is cold outside. We have stayed on top of the fluids, done fluid changes, and replaced the filter. I am out of ideas except for one and that is trading it in. Can any of you shine a light on the issue?