I wouldn't do it. I would sink money into the 04 to make it better than taking the hit on a newer truck. Fuel mileage is MUCH worse than the 5.9 and the extra power is not worth it. Of course the only 6.7 I drove all over the country was an 07 G56 6-speed, good power, horrible mileage, terrible transmission, and that rotten egg smell and constant burning off of the catalyst. I won't even consider a 4th gen Cummins at this point. Is yours the 305 555 or 325 600?