Heads up new '05 Duramax owners.
I recently installed a Magnaflow "Cat back' system on my '05 Chevy Duramax. Truck ran great (approx. 40 miles) until the check engine light came on and the rig switched to what I'll refer to as 'limp mode'. Dealership mechanics said the computer read a 'low exhaust back pressure" code and reset the system.
Approx. 70 miles later, the check engine light came on again, same indication. We removed the Magnaflow cat back system, re-installed a stock exhaust system and have not had any problems since.
I've been told by Magnaflow that the application of a performance chip may (emphasis on that 'may') correct the problem. The new '05 rigs have a very sensitive sensor system. Advise hold off on any exhaust system modifications until further research is done.