You can swap in a quality cummins / duramax / powerstroke of your choice with significant time and money invested into it. However, if it was up to me, there are a ton of things you can do to your 454 to get good torque/hp numbers for a lot less time and money. You can even swap in a full race engine and built tranny for less than it would take to get a quality diesel in your truck. Shop around on racingjunk.com I have gotten engines from private machine shops with quality internals and professionally built with warentee's for less than a summit/jegs crate engine.
Dont waste your time with a 6.2/6.5
Dont waste your time with a 6.2/6.5