LimeSDR GFSK Output very low power

Hi, I am currently trying to get my LimeSDR-USB working with a gnuradio implementation of GFSK modulation. I am currently getting an output that is very low power and was wondering if anyone had advice on how to improve the output.

TX gain is set to 50dB? Maximum is 73dB. Also, TXLPF can be set to 20 or 40MHz (second harmonic is at 870MHz). Not sure is it even possible for LimeSDR Sink(TX) block or is it performed automatic.

Have found that center frequency can jump around when gain is set to the highest levels. In terms of TXLPF, thanks for the tip.