I have a 2004 envoy slt xl with 79,xxx miles, and its been getting about 12.7 mpg when it used to get about 15.7 mpg. This is mostly city driven. Sinced the water pump and thermostat broke down its been 12.7 mpg. The water pump, thermostat, coolant temp sensor, ac delco plugs, fuel pressure regulator, k&n air filter, fuel filter, ac deco o2 sensor has been changed to new ones but still not improving the mpg. I also put in some fuel cleaner too but still not improving. I clean the throttle body too but samething. Im planning to change out the cat converter or just cut it off. What else should I do next?
Any input will help, thanks.