Hi everyone, I am looking into buying a 2500HD with a Duramax. I have a few questions about the difference between the LLY and LBZ. I have read that in stock form the only difference between the two engines is the tuning. Once you use an aftermarket tuner they make the same power levels. Is this true? Also I read one place that the 2005 and newer trucks have the 6 speed allison tranny's in them. Another website said the 2006 and newer have the 6 speeds and the 2005's only have the 5 speed. Which is correct? Any input or advice is appreciated.