Pretty limited info, but I'd say the impellers have nothing to do with the engine RPMs. That doesn't mean they are good. Just not part of that problem. You can inspect them yourself. If they look like they've been spitting rocks, you probably need new ones.
No comment on the wiring.
Carb rebuild sounds right for the running problems. No idea what the high pitched suond would be.
Thanks for the info. It was a carb rebuild. The boat runs great. Many thanks to Ecklund Marine in Oshkosh for their help. Kind of skeptical of Trackside in Eagle River on their diagnosis techniques.