I thought it would be something like, that since you're here asking questions about something that definitely should be warranty work.
Have you checked for trouble codes yet? Strange blinking on the dashboard clock? Anything like that?
Due to the nature of your problem, there's probably not a code thrown. But sometimes you get lucky. And at any rate, that's the best place to start.
I read the question differently; in that the original poster was asking if a 10 mpg limit could be set, even if the belts are being worn - like if children are using the UTV. If this is the question, then look here:
https://utvspeedsafe.com/
The default setting is 15 mph, but it can be adjusted.