I just bought an 2006 2500HD crewcab / 6.6L / Allison 6 speed trans. and while talking with my insurance company about adding it to my policy they said the VIN I gave them is not for the turbo diesel. The 8th character is a "D" and they said it should be a "2".  The truck is definitely a turbo diesel.  I went out and checked the VIN on the truck and it has a "D" in the 8th place on the VIN.  Anybody ideas how this could happen?  

I bought my 06 Duramax new in Southern California. When I spoke to my insurance about adding it to my policy they discovered there was another truck with the same VIN number. Turned out my truck originated from an assembly line Canada where the other truck is from the states. Somehow my truck ended up at a dealership in California. Its possible that something like this may have be your problem source. Or then again, if you bought it used, maybe the last owner converted, although higly unlikely.