I wish I could afford the bed space for dual 6" stacks. As stated above, I have a single 6" stack now and love it. Mines actually 4" from the turbo to the BD brake, exits the brake to a 5" expander, 5" pipe through the bed to a single 6" stack (Bullhauler style). Chris T. has dual 6" stacks on his 2500 and they look and sound real sweet. There are pics. of both of our trucks in my gallery (readers rigs). I needed a transfer tank so that is wedged in the space that the other stack would rest. If I ever decide to give up that tank, I will have dual stacks for sure.
Scott W.