Will not shift out of gear while running – intermittent issue

I am looking for some suggestions on troubleshooting my 900xp. I was riding it yesterday (hills, some mud, mostly dry), and a couple of times it would not shift out of gear when I stopped with the motor running. If i turned off the engine, it would shift normal and easy. Turn the engine back on it and it would run and shift normal. This happened a few times during the day.

I also noticed that the clutch would not disengage sometimes when going down steep hills. Normally, I have to tap the throttle to keep the RPMs high enough to keep the drive engaged and use engine braking on steep decents. Yesterday, it would sometimes just stay engaged when it normally would not.

I have not had a chance to take the cover off and inspect the belt yet. I had some friends over a couple of days before I rode. They took it upon themselves to ride it around my yard before I could check them out in it. They rode in High the whole time at low speeds.

Any advice is appreciated! Thanks!