Just purchased (traded Honda ATV for) a 2005 3010 4x4 mule. I love it so far but have these issues: top speed seems to top out at about 15mph. does not idle for very long without dying.

This mule is 8 years old and only has 107 hours on it. I suspect that the little use it got, and sitting with ethanol gas has gummed things up.

I drained the gas, put non-ethanol gas and Lucas gas treatment in. There is some improvement, but not much.

Any suggestions?

 

I would pull the carb and do a complete cleaning. Checking float height etc. Pull screens and verify that they are clean. Sounds like you got a nice ride.