Well your 4000+ posts don't appear to have helped your reading comprehension... The code, and the sensor work fine as is with an Arduino Uno. So the CODE is not the problem. Since it works with the UNO none of your comments are relevent.
So if the CODE is not the problem, you must have already solved the problem. Because if your idea about the processor clock speed would have been correct, that would have been a code problem. And I checked that with the library I linked, so I'm sorry but my comments are relevant.
So is that clear enough for you pylon? Since you would need to 'google' the library/setup you don't have the 'experience' my question was asking for.
It's not a good idea to affront the people who want to help you in the forum. My starting comment was about something that is clearly mentioned in the sticky note at the top of the forum. If you read it and acted according to it, my comment wouldn't have been necessary.
BTW, I did successfully use a DHT-22 sensor on a 8MHZ 3V3 ATmega328p (OK, it wasn't a Pro Mini but a custom board, I don't think that this difference is relevant), so I had the impression that my experience is not that way out of what you were looking for.