2000 sportsman 500 doesn’t have much pep.

So I’ve had a 2000 polaris sportsman 500 for about 7-8 months now. When I bought it the guy said( a 4 wheeler mechanic) it had barely been used and had just sat for a while, and he went through and fixed it up. Then he sold it to us. The other day i was riding it and seems like it doesn’t have near as much get up and go as it should. Could just be me, but any ideas on that? And also there’s a kind’ve a creaking or popping noise coming from one of the joints or shafts or something up front. Any ideas on that? I don’t know much about 4 wheelers.
Thanks.