Hello, I'm Chris. I will do my best to answer your question fast and accurate using the info you have provided. Thanks for visiting Just Answer.The fluid level needs to be at the full mark when idling in park hot, not just i nthe crosshatch. There many differnt things which can cause a harsh 3-4 shift. Below is the symptom chart from ford for this issue and I have highlighted the common causes, all of which are going to result in a overhaul needing to be performed.