Hi,
Are both SSIDs using both 2.4 + 5GHz? If so, when you connect to each SSID do you connect on the same frequency?
For more information on your connection status on a Mac, hold down the alt (option) key and click on the Wi-Fi icon in the Finder menu bar. This will tell you what channel, frequency and data-rate you are connected on.
Thanks,
Darrel.