The 2008 year was the reason I switched to a gasoline truck. I didn't know about the DPF's being added. I ordered a nice Ram in the late summer of 2007. A little later I got a call "They quit making 2007s. Your only choice is to accept a 2008". I don't remember anything about any changes on the $ but there must have been.
I ordered the 2008 and, just before it came in, discovered it could ONLY used ultra low sulpher diesel (if memory serves correctly).
I searched and could only find one fuel station within 25 miles that had ultra-low sulpher diesel. The Manager of the dealership told me "They will all have it soon. I don't know if "soon" means 6 weeks or 6 months. Certainly not more than a year or two".
He agreed that it would be unrealistic to expect me to go thru with a deal on a truck that I couldn't fuel.
He gave me back all my deposit and I ended up getting a Ford F150.