You are working on a very similar project like me. Your automatic gain control is not active because the LimeSuite block in gnuradio does not support it.
See this post
The problem is that the RX is not configured sensitive enough (which is why you need AGC) and that, if you use two boards, you need synchronization. This Wiki page @ the gnuradio wiki helped me a lot.
https://wiki.gnuradio.org/index.php/Guided_Tutorial_PSK_Demodulation
So it is possible to transmit with a LimeSDR, but youre probably gonna need to put some effort into it. I’ve been working on it for some time now, but then again, I am a complete noob in this sector.
-Martin