I cant seem to keep the radio on the screen as a default it stays on Nav all the time any suggestions it a rx350 2010

 

Had that problem in my 2013 too -- was driving me crazy! My fix is in the Customization Settings--says something about reverting to the previous screen - you have to turn that off. Like to have never figured it out!
Good luck!

 

In General Settings, there is an "Auto Screen Change". I think turning that off will get what you want.