Check out murf.ai, that service works similarly to what i described

I think this is more likely a task for Python. I haven't done anything like this myself, it's just the approach I would start with.

I'm not sure how I'd go about syncing it, but would this be an adequate workaround:

• break apart your script in small chunks by time stamp
• generate different tts recordings off of each time stamp
• generate an audio file that inserts each of the produced recordings at their respective time-stamped location
• replace the audio of the recording with your newly produced recording

Could you speech-to-text your lecture, collecting timestamps, do the same with TTS and automagically sync that way?