I assume you’re using an All in one board, since you talk about a teensy. Somebody more knowledgeable can correct me, but I believe you need to leave UART 1 alone, as the teensy communicates with the F9P over UART1 at a baud rate of 460,800. If you have a AIO micro board with single, you can export your nmea from UART2 on one of the two pins highlighted in white.
This post, might give you some ideas.