I have a 2005 Trailblazer with the 4.2L i6 and I'm thinking about buying an aftermarket muffler/exhaust. My question is: what kind of muffler or exhaust setup can I get that will not decrease my MPG? I have seen other posts on this forum about people installing aftermarket mufflers and saying that they lost mpg. I've also seen a lot about how this engine needs enough backpressure and sometimes modifying the exhaust system will cause a loss of too much backpressure. I'd like to get a bit better sound from the exhaust but I'm not sure if this is possible without sacrificing fuel economy. Please let me know if there are any options or if I should just keep this factory.