2003 Honda rincon 3rd gear not working right

I just bought this a few months ago. It’s an automatic and has the switch to use it as a standard. 1st and 2nd are working fine but as soon as it hits third it will run ok until it gets to 40mph then it will act like it hits the governor. And other times I can get it up to 55mph with no problems I’m kinda stumped so any help would be awesome