Comparing Pluto blocks for GRC 3.8 and 3.10, I notice that the Tx power is about 25dB lower for the newer 3.10 version of the blocks.
This can be seen with a minimal flow graph of a 1v signal source driving the sink and hooking the source up to a QT Freq sink. I use 430 MHz, the RF loop back cable and set Rx to 10dB manual gain. With the GRC 3.8 block, and 25dB of Tx atten I see ~-30dB on the Rx spectrum display (arbitrary units), where as for the 3.10 block the same Rx display is achieved with 0dB Tx atten.
I found the same using a spectrum analyser; for 0dB Tx atten, the GRC 3.10 block outputs -29dBm where as the 3.8 block outputs -5dBm (both measurements via a 6dB coupler)
Just copying a 3.8 flow graph to the 3.10 environment unfortunately does not work, so you do need to reproduce all the parameters by hand. So there may be an error there, or some other setting I have missed. But I have checked carefully and boiled it down to a minimum flow graph.