i believe it is time to tune up my car cuz it hit 80,000 miles. anyway, i'm going to replace my o2 sensors. someone told me that replacing these could give me 20% more power because of the cruddy old ones. anyway, is there a certain o2 sensor i should get, or are all o2 sensors the same? and do you guys know where i could purchase these o2 sensors for the cheapest? oh, one more question-who will install these, a muffler shop?