Hi Amanda,
Adjusting the transparency using the slider under the Places panel should work. Selecting the actual overlay and not the folder containing it may help.
Could you provide a link to the file you are using?
Also you say "satellite and map versions". Google Earth Pro has no built in map version, are you using an overlay to get the map view? Or the "open in Google Maps" option? That probably won't work very well.
You may also want to turn off the 3D buildings layer to get a better view of the overlay.