Why is my RPM too high at lower speeds and car not shifting into third

Got a used engine under 55k mikes installed at auto shop due to a failed piston compression in my previous one. Get the car back a week later told it’s fine to drive. Come to find out that the RPM’s are way too high going a slower speeds. Took it in again and had them check the transmission and they installed a new filter and topped off fluid. Still having same issue but they told me that the car needs to relearn when to shift since but i drove it over 20 miles at various speeds and is doing the same thing. I told them to check the ECU but insisted that it just needed to relearn. What is the issue?