I was just going to laugh at this and move on but had to comment.
The 6.4 is a crap engine, it's actually worse then the 6.0 I think. We've got a ton of them and they have ALL been in the shop for major repairs before 50K miles.
The 7.3, 6.0 and 6.4 are all built by Navistar. The new 6.7 is a Ford in house designed and built engine.
If I were you I wouldn't do anything to the truck as far as DPF deletes as the engine will still have issues. You can buy a 7 year 200K mile engine warranty for under 2 grand that will cover the majority of components that fail on these.
The biggest issue was that the 6.4 was designed as a interm engine to meet emissions in a short design time frame. It's biggest issue is cooling, if you look 90% of major failures are caused by cooling system failures (EGR, Oil, etc). The engine just generates too much heat for the cooling system that it is equipped with.
If you look at the new 6.7 engine Ford is now using a two separate cooling systems. One low temp and one high temp, I believe this to be their attempt a controlling their heat issues and thus failures. When I asked this question to a Ford engineer we were meeting with his face went blank and you could read that he knew they had cooling issues with the 6.4 and they were trying to prevent that with the 6.7.
The other design issue is that the 6.4 had to combat emissions with more fuel and no UREA. The new 6.7 is using UREA so it does not have to dump fuel into the combustion chamber to create enough heat in the DPF to burn of the excess soot and reduce NOx. There is no doubt that the fuel dump in the 6.4s causes a great deal of these issues.