In the X-plane 11, in the default B738 with P2A v.2.3.1.1, SayIt will read off and the practice will recognize my voice, but it will not work for the 'ATC'. The program works with the 747-400, so I know it's installed correctly and everything is setup. I thought it might be a plugin but I disabled all but XPUIPC and the built-in Lua that runs the gauges and still no joy. Is there something I'm missing?

Settings, like the call sign, can cause ATC not to work. 

Different aircraft have different Battery and Avionics switch options.  Try checking the "Ignore Battery Switch" and "Ignore Avionics Switch" settings in Config.

Dave

Thank You!!! That was the issue.