"I recently replaced my Flowmaster Muffler with a new Aero Exhaust 3535 for my 2004 Chevy Duramax, based on several friends who have also used the Aero Exhaust. I have seen an impressive increase in horespower and especially torque off the line, but where I really noticed the difference was in the exhaust temperature and the overall fuel mileage.I have used several different companies mufflers and have found that Aero Exhaust is by far the best muffler out there. I was a big fan of Flowmaster, but definetly am a convert to Aero now."