Sometimes, when my car is fully warmed up, it will up-shift harshly. Why?

What is your question?

It does not always do this. It may go days before it does it from one time to the other. Only when it gets warm from a lot of stop and go. I had the filter and fluid changed 3 months ago and it seemed pretty good for a month, then in the second month it did it again, only for a couple of days, then back to normal. Today it did it again. Just can't figure that out.