I recently bought a 2005 ss and it sounded pretty bad, only mod had a magnaflow muffler, a day later I get CEL light it was the infamous po171 code so I sprayed down the maf with carb cleaner, tried resetting it by the battery, and after having the code erased a few times, I took it into the dealer. Where the dealer looked up the history and found it had never had the ecu reprogrammed. And that the fuel trim could of been from differen't brand gas. After they got done with it the car never had the same sound to it backfiring or w/e shifting out of first except sometimes. And my mpg had gone down from 35mph to below 30mpg. I drive back and forth on highway everyday and use cruise control. My question is that can is there someone that can tune it to have good cruise control mpg like 35mpg. IDK if it was bad driving on the car b4 maybe it was to lean whats the average mpg highway I should get if im pretty much all stock?