I've been running my 12 valve straight piped. Maybe I'm accustomed to the bark and raspy tone, because the 4" x 30" FTE resonator really made the truck tame while retaining the signature 12 valve sound. The little sucker made a big difference with my 95 3500 with a right rear turn down. The droan is gone, I hear wind noise and turbo whine over the exhaust now. Still plenty loud at idle, but on the road the raspy scream under boost is muted, its more of a pleasant turbo whine. Yet it retains the big rig loudness. Hear lots more engine sounds now, I can hear an annoying belt chirp or something squeaking at idle, valve clatter etc..
The biggest difference is off idle, the loud aggressive bark is tamed. I can go through town without drawing unwanted attention now. Its actually louder at the front than the rear, I can talk at the tail gate with the turn down blowing dirt around. I still yell trying to talk at the front bumper with the engine rattling, but its a 12 valve.
No change in performance, still hits the same boost numbers. EGT appears to be the same or very close. I can hit 45 psi playing, I do try and keep my foot under control though. 35 psi comes easy just like before. The 2700 rpm pulls at 35 psi are so much better, headaches gone. I can roll down the windows and hammer it without my ears aching. I'm happy in case you missed it. Not to tame, not to loud... just right IMO.
The biggest difference is off idle, the loud aggressive bark is tamed. I can go through town without drawing unwanted attention now. Its actually louder at the front than the rear, I can talk at the tail gate with the turn down blowing dirt around. I still yell trying to talk at the front bumper with the engine rattling, but its a 12 valve.

No change in performance, still hits the same boost numbers. EGT appears to be the same or very close. I can hit 45 psi playing, I do try and keep my foot under control though. 35 psi comes easy just like before. The 2700 rpm pulls at 35 psi are so much better, headaches gone. I can roll down the windows and hammer it without my ears aching. I'm happy in case you missed it. Not to tame, not to loud... just right IMO.