Q: 07 hyundai sonata 3.3 limp mode

Check for any OBD-II stored trouble codes that might provide clues. If you carried over your sensors, such as the transmission speed sensor, and other controls to the replacement transmission, I would first look for a fault with those external controls including the possibility of a bad wiring harness connection or a missing ground connection (be sure all original grounds were re-installed and are good). There are engine controls, too, that can cause limp mode to set and those have to be checked. These include the manifold absolute pressure (MAP) sensor and the throttle position (TP) sensor. To resolve this problem you are having, the service to request is a shift diagnostic - limp mode. If you request that service the responding certified mechanic will come right to your location and get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.