Q: engine operating at reduced output

Hi Pat...you should request a check engine light diagnostic during which a certified mechanic will download and interpret any stored diagnostic trouble codes. If there are no stored codes, one strategy is to scope the engine, that is evaluate the cylinder secondary firing patterns. Typically, this will give the mechanic an indication of whether there is a fuel or ignition system problem, or both. It is also possible to use OBD-II data to look at, for example, long and short term fuel trims to determine whether, in fact, the engine is running properly. Fuel trims outside of a certain range are tip-offs that there is a problem and will give the necessary clues as to which engine management "system" should be looked at. These are all diagnostics that the mechanic will rely on if you request a check engine light diagnostic.