I had a 96 scrambler that I bought cheap because it had similar symptoms. When I got it home I immediately checked compression, it was 101. So I tore down the top end and found the problem. Both skirts on the piston were cracked and had pieces missing off of them and the rings were also a bit sloppy. The cylinder only needed a slight honing. I attribute this to excessive cylinder heat. So I started looking and sure enough I could see where the previous owner had replaced a coolant hose. Instead of buying the factory pre-bent one he rigged on a homemade one with plastic elbows that still leaked slowly. This told me that theres a good possibility that he ran the machine hot before.
Anyways, my machine still had enough compression to run but the damaged skirts accounted for the power loss. Its easy enough to strip down the top end just to check it. Maybe itll be fine and then you can at least rule it out.
2004 Polaris Scrambler 500 HO 4x4
2005 Kawasaki KFX400