Clutches slipping?

Ok guys so I have a 1993 Honda 300 fourtrax 2wd and here lately it has been slipping in only 4th and 5th gear. I automatically thought of it being the transmission but I decided to do some further investigating and decided it is not the rearend and it has to be the transmission or clutches. I’m leaning towards the clutches only because it’s slipping in high gear and only when you accelerate. Once you get up to speed and have higher Rpms it runs fine. So, what do you guys think?