A solution from fellow Run8 user CT:

"Great news!!! I figured out the issue of what was causing the performance drop. After checking the Run8 event log, I happened to notice that upon startup, it was mentioned that the allocated RAM was only 15mb. I was able to allocate more RAM/change the graphics priority of the application by changing the setting of Run8 to “High Performance” in system settings. Now, I’m able to run what was the most performance-heavy area of Waycross with a stable 70 FPS, a huge difference from what was only 30 FPS because of the tracks. When I look directly at the tracks on any route, I still maintain above 70 FPS."

System Settings > Display > Graphics

"Then, it will provide a list of apps that have custom options in regards to performance. Under where it says “Add an app”, I clicked on “browse” and selected the Run8 application. Then, it was added to the list. I then clicked on Run8 in the list and pressed options where it will provide 3 options for “graphics preference”. I selected the “high performance” option which will use my GTX 1660 Ti GPU and not the AMD Radeon one used for power saving. I believe my issue was that the “Let Windows Decide” option is used by default, which limits Run8’s usage of RAM."