IMO there's no substitute for cu.in. Yes the 3.5 is a great little engine, but Ford knows it won't work in their SD line or it would be there. There are lots of high HP/TQ engines in cars. Look at some of the 600+ HP motors like what's in the new Mustang. 662hp and 631tq. Why not put that motor in a truck? Probably cause it won't last for someone towing 10-15,000 miles a year. There's no difference between what the 5.8 Mustang engine and the 3.5 EB are asked to do. Each is designed for it's own application.