I can tell you from experience a glass pack sounds horrible on our 3.6L trucks. I have tried a glass pack, magnaflow, 40 series flowmaster and 70 series flowmaster. By far the best sounding is the 70 Series Flowmaster with the resonator on which is what I currently have now with a K&N Blackhawk Intake. Its the only one that didn't give it the high pitched 4 cy sound or very annoying drone. It sounds clean and deep throughout the whole power band. The glass pack would get higher pitched and more annoying as the rpms got higher.