I'm playing on Windows 10 with a 1080p monitor. I'd rather play with the original aspect ratio with the black bars on the sides rather than playing with the resolution stretched. Thanks for any help.

I figured it out. Here's how, in case anyone else has the same question from a Google search.

1. Right click anywhere on your desktop, click on NVIDIA Control Panel.

2. Go to "Adjust desktop size and position" under "Display."

3. Change Scaling to "No scaling."

4. Change "Perform scaling on:" to "GPU".

5. Check the box for "Override the scaling mode set by game and programs."

6. Click "Apply."

Doing these steps let's you run the game in 4:3 without it being stretched.