Just recently joined this forum so I don't know if I'm lucky or what. Read lots of stuff about CEL being on and codes when removing stock exhaust. Well this past weekend I pulled everything off and put on an MBRP Turbo Back system. Have driven over 400 miles since then. CEL light has never came on and today I had dealer check and there's no codes nor pending codes. One thing I did do was put the MBRP muffler on the opposite from what's recomended in the instructions. I did this at the direction of the dealer where I purchased. He said that doing this would provide enough backpressure to keep my system happy.
I really like the sound. It's not overly loud at all but has a nice throaty rumble to it. My kids love the hissing sound fromt he turbo when idling. My dealer even asked me how long it took to install and when " was I going to chip it".

That is a good idea I might try changing the direction of my muffler then... so you put hte muffler on with the "cups" facing the motor?

Turbo, yes that's how it's mounted the opening of the cups face forward instead of backwards. I don't know if that's why I"m not getting any codes but I don't see how it could hurt either. It seems that most of the codes are caused by not enough back pressure. It didn't seem to me that just doing that would make a difference, but the dealer that sold me they system said they've put lots of these on the Duramax and haven't had any problems.

thanks for the tip.. if I have time I might try that this weekend