”Mules” have different models… Ours runs almost 50 mph. It has fantastic suspension…but I consider that speed a roll-over hazard. I don’t recall how…but my son has programmed a “speed limit” into it which limits it to 25 mph for when HIS son…my grandson… drives it. (maybe that’s a factory option…? maybe yours is inadvertently “set”….??)I don't know.....the Mule I had was limited to 25mph.
I'm sure there is someone selling a device that will remove the limiter. I'd be a little hesitant because you could easily over-rev the engine.