Drive train issues.

Hola everyone,
First time posting.

I just upgraded from a 2006 Sportsman 800 EFI to a 2015 Sportsman XP 1000. The quad has just over 80 hours on it.
When I test drove it on dirt, it seemed like it started revving up too much before the drive train engaged (Around 2250 rpm). It wasn’t that bad. When I got it home, the revving and delay on engaging was more prevalent in the concrete driveway. Additionally, there was a slight clunk coming from the rear end, and it would surge a bit after the clunk hit… like it was locking into gear. I don’t hear any grinding and all the bearings seem tight on the Diff.
I know they are belt driven, and have two variable pullies that give you your speed. What I don’t know is what might be causing this issue. Any ideas?

Second issue I am having is that when I am up at speed, it seems like it is pushing to the right. Do you think the drive train issues I am having are causing this push, or is it a separate problem?

Thanks in advance.