Lots of Deisel swap advice and info over at
www.4btswaps.com

If you want to go any faster You'll probably have to change the rear axle gears, you can calculate that sort of thing here.
http://www.onlineconversion.com/bigger_tires.htm

With the big increase in power(and speed?) you may also need/want better brakes.

A duramax swap will cost some money...
Here's one of the best resources for performance Duramax stuff and I think they have stand alone computers for them. (at least from what I hear/read... no personal experence)
https://www.pacificp.com/

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-