Ceiling Fan is very slow after 2 years operation
Does your fan have sealed bearings or ball bearings ? 
They can get dirty and cause mechanical drag.  there may be other rotational loses coming into play.  try a dry lubricant from a bike store if there are parts that need it.  there could be a issue with the rotor or stator effecting the flux transfer
 to allow the motor to spin

What happens if the fan motor is plugged into the 
wall?  does it run full speed? if it does there may be 
a fault in the electronics of the controller board

hope the idea help