I don't think putting a diesel in the GM LD trucks would be as easy as some think. First, the 4.5 is old technology and I don't think it would be competitive with the newer generation engines. I think it would suffer when compared to newer engines with a lack of power and/or poor fuel mileage.
Also, I think the Ram is selling well because their trucks have a long history of having dependable diesels. On the other hand, GM's attempt to put diesels in their LD trucks suffered greatly because their first attempt was a disaster because of a problem engine. I know many will say that the GM fiasco doesn't matter because it was so long ago but many of us lived through the disaster or our parents did when we were young. We're still buying trucks and many of us will wait a few years after GM has a diesel before we will take a chance on one. We didn't wait the first time and we were badly burned.
Also, I think the Ram is selling well because their trucks have a long history of having dependable diesels. On the other hand, GM's attempt to put diesels in their LD trucks suffered greatly because their first attempt was a disaster because of a problem engine. I know many will say that the GM fiasco doesn't matter because it was so long ago but many of us lived through the disaster or our parents did when we were young. We're still buying trucks and many of us will wait a few years after GM has a diesel before we will take a chance on one. We didn't wait the first time and we were badly burned.