2007 Sportsman 500 EFI, heats up when I ride. I keep a close check on it, don't let it get too hot and make sure it cools off properly. Cooling system working correctly, radiator clean, coolant level full.

A friend mentioned the water pump impeller might be bad. Not leaking at the water pump so I'll check it.

Any one heard of this or experienced problem with impeller? Replace impeller only or water pump too?

I'd replace the whole pump. If it's old enough for the impeller to go bad, there's no reason to think the bearings aren't ready to go, too.