Gm isnt known for making any good diesels that I know of, maybe somone has some personal experiance with them that liked it. Montgomery is right about the ford 7.3 being king but I think the new ones are good too. Also I hear great things about dodge. I think thier cummins engines and I was talking to someone that had a new one outside of his truck while it was idleing and it was so quiet I had to ask if it was a diesel!