[Diesel_Dave]

Regarding your goal stated in the original post (40 MPG) I would say its doable but don't get too far ahead of yourself. Take things slowly. Do one thing at a time. Research mods before you do them so you understand the benefits and risks. Perhaps most importantly, keep good records. You're off to a good start in the mid 20s. The path to 40 is a bunch of small steps of 1 or 2 MPG (or less).

I'll agree with oilpan that a newer turbo would probably help quite a bit. I'd have to look Ito it a little more to see what your options are. One easy option might be a junkyard turbo off the common rail 5.9s (mid 2000 model years). That wouldnt be a bad option and shouldn't be too expensive. A better option might be a turbo of the industrial 5.9s of the same era. That turbo would be better suited to the lower rpms you will run. The 5.9s in the Dodge trucks spin a lot faster than the off highway engines, primarily to show a high HP rating, wheras industrial engines want lots of low end torque.

Like oilpan said, as long as you're talking all mechanical turbos, the swap is pretty easy to do.