My 2019 has the same 3-4 issue. It feels like the brakes come on or you just left completely off the gas and the rpm's will climb couple hundred rpm's before shift is complete. Took it in to Ford and had them reset shift tables. Haven't had the issue since, only been a week and this doesn't happen every time so not saying this fixed the issue. It only happened to me if I was lite on the throttle and when it did happen it was the 3-4 shift. Also, my drive way is 1900' long and I drive out slowly till hitting the main road so temps should be getting up some compared to someone just getting on the road with no warmup. This isn't normal no matter what people say, why not between 2-3 or 4-5. Maybe a mapping issue or trans issue but I wanted it document that I'm having this problem.