ok i was getting about 15-17 around town...and 19-20 on highway with my 2000 Silverado 5.3L. I recently got a Flowmaster 40 series muffler, and ive cleaned the fuel system, throttle body, MAF. And since all that...im getting about 11-12 now...all together. It sucks. What do yall think it is?
Thanks
This is the exact opposite of whats suppose to happen when any of those things are done.