ive been puttin 10 doolars of gas in my car everyday ive got a 3.4 auto with many performance parts to help my gas milage but i seem to still have bad gas milage ive put in a moroso airkit, pacesetter headers, magnaflow exhaust new spark plug and wires o2 sensers, TPS, IACtires allignedand ive even been babing it.what else would be given me bad gas milage i have 135000 miles it runs fine. it does have some abnormal vibrationsit i dont notice any power loss ive been havin trouble with my egr valve but idk if that give bad gas milage. in town im prob gettin 15 mpg