External Monitor display problems on OS X 10.11 El Capitan

Is there a similar update for the Mini DisplayPort to VGA Firmware v1.0 that's compatible with OS X 10.11? I've been having problems with my monitor ever since I installed El Capitan. External monitor flickers constantly when set to 1920 x 1080 resolution. I've read elsewhere that some people had success with their external monitor screen flicker issues but they were running Mavericks.

Using MacBook Pro 13" Early 2011 (I know... 😝)