The problem with the fuel pump for some years is caused by the bends and ensuing kinks in the SUCTION HOSE ONLY, that attaches to the bottom rear of the crankcase. The fuel pump stops working and shuts the engine down so fast that it doesn't have time to burn the pistons up. The original stock black rubber hose with a fiber cross weave, has a far less tendancy to kink when it gets warm. The Polaris update that was sold to me was a red plastic hose. Of course, the dealer may have deliberately sold me the wrong hose for that as well.
The hi temperature o-rings that I was referring to, sit on top of the cylinders and below the cylinder head.
Defective hi-low beam switches also cause RPM problems, believe it or not. Defective CDI boxes will also cause RPM problems. I have a new one for sale that is guaranteed to be fully functional, for $50. Polaris will gouge you about $340 for the same item. Never hurts you to carry an extra around for an old sled.
Thermistor wires may be wearing out. Some Polaris dealers like to bend the wires over as they come out of the top of the thermister, in order to sabotage the sled and cause premature engine failure. Which may then kill you when you break down 30 miles from your ride home, in a snow storm.
A stator that is going out may miss now and then and may have trouble idling at the same RPM's.