Is anyone having problems adding a new vehicle?

Let's fix your vehicle issue, Jleonard.

There are times when your browser is full of frequently accessed page resources that can cause some unusual responses and odd behavior. You can log into your QuickBooks Online (QBO) account in a private window (incognito). This mode doesn't save passwords, cookies, and your browsing history, making sure it's free of issues. I've provided the shortcut keys for you to follow:
 

• Press Ctrl + Shift + N (Google Chrome).
• Ctrl + Shift + P (Firefox).
• Control + Option + P (Safari).
• Press Ctrl + Shift + N (Microsoft Edge).

Once signed in, double-check if you can now add a new vehicle. If so, return to your default browser and clear the cache to speed up the loading process. Every so often the cache becomes overwhelmed with older data which can potentially cause viewing and performance issues. Clearing them refreshes the system, and you'll be able to work with a clean slate. However, if the issue persists, try using other supported browsers.

Furthermore, you may also notice inaccurate trips when using the mobile app, learn how you can set them up and be able to track trips accurately. I've added this article for more details: Fix Mileage Tracking Issues In The QuickBooks Online Mobile App.

You can always get back to me if you have any questions when tracking mileage in QuickBooks. I'm always right here to assist you further. Have a nice day!