Subaru Repair: Outback H-6 engine misses, fuel mileage, typical issues

Question
My 2003 Outback H-6 has never run very smoothly.  Sometimes much worse.  Jerks under mild acceleration.  Delaware has 10% alcohol.  In past, a bottle of fuel treatment seemed to lessen the problem.  No engine lights.  Mileage in low 20s steady.  Use premium gas.  Possibilities?  48K miles.

Answer
Have you compared it to a like vehicle?Subarus are not the smoothest feeling vehicle out there.Just the best.The fuel mileage looks about right for that configuration.The h6 has been a good engine so far and there really isnt any typical issues as of yet.Im not saying that your car doesn't have an issue only that there is nothing typical i could lead you into checking.The car would have to be diagnosed by someone who knows Subaru.My first guess would be an o2 sensor.