careful of how you set your exhaust up... you have a heavy truck. loose any low end torque and you'll be crying @ the pumps. I wanted duals on my 2000 & ended up having a 3" in/dual 2.5" out flowmaster kit installed... lost alot of low end torque but the top end was improved significantly. took it to a shop and had them install some reducers to put the outputs at 2.25" which was slightly more flow than a single 3"... worked out awesome, low end torque came back (along with 1~1.25 mpg) and all was good again...

 

How long did you give the pcm to learn the new setup before you had the reducers put in?