Transmission kick-down bang

Okay, a few things that should be checked. Pop the negative cable off the battery. Now unplug and spray the throttle position sensor connectors with contact cleaner and reconnect. Next check that the solenoid pack on the transmission is not leaking, they wear and crack. If neither of those looked bad reconnect the battery cable and take it to a transmission shop or dealer. Have them scan the transmission control module for any codes (the transmission module can have codes that do not turn on the light). If no codes do a transmission relearn procedure on it and see if it now shifts okay. I have seen a few where a power surge or something has caused the TCM to act strange. Beyond that a bad control solenoid could be sticking and causing it to shift hard. The shop should be able to see if that is the problem by triggering the transmission controls during testing.