Just a guess, since I don't have one myself...
The throttle position sensor is probably the main input to tell the trans control module you want to pass someone. Maybe somehow that signal is getting to the engine part of the computer, but not to the trans control part?
IDK if that car has a separate Trans module or if it'* part of the PCM.
You'd think that if a solenoid has gone out that it would throw a code...
Sorry I don't have much experience with your car, just trying to help - come up with possibilities.