Check to see if Safari is running in 32 bit mode. Right or control click the Safari icon in your Applications folder then click Get Info. If the box next to: Open in 32 bit mode is selected, deselect, quit then relaunch Safari.
Sometimes uninstalling then reinstall the Flash plugin can help > Troubleshoot Flash Player | Mac OS
Very important to uninstall the original plugin first.
I also switched to a faster internet provider.
Connection type? Wired or wireless?
Might want to pull a test of your ISP speed. Depending on the type of service, you may have a shared connection (common with cable) and your neighbors' usage can affect your actual performance. If one of the neighbor kids is hosting an online game or a big file sharing site, your performance can suffer. I use this speed tester:
I have cable internet that's wired. The speed is 25m (it's about 3 times faster than when I had DSL). I think you're right, Allan about the shared usage. In retrospect, I usually have the problems between about 6-9 pm, which could be peak hours.
As far as Flash, I may not have uninstalled Flash before updating it.
Thank you both.