Are you getting any codes? If not I would run some fuel injection cleaner and see if that helps. I think the one called techron by chevron is the one of the better ones. Try this:
1. Run Tank down near empty
2. Pour in Injection cleaner
3. Fill tank with HI-test good gas.
4. Run that tank down to empty or close to it
5. Fill up with only Hi-test gas
6 Run that tank down
7. Use one more bottle of cleaner with hi-test gas
This should help and hopefully solve the issue, if not then maybe it need a good tune up. Plugs, wires, filter etc etc.
As for the fan, sounds like you need a new switch if its only working on the higher settings.