I have a 2004 2500. It has 46000 miles and I have a underbody vibration. I took it to the dealer and they said I have a blown baffle in my muffler. I went out and got a Magna flow muffler and I still have the vibration. It only happens when driving around 2000 - 3000 RPM. When I have it in idle and rev it up I get no vibration. I checked my underbody heat shields and they are all tight. Does anyone have any idea's what it might be?