Keep your fuel clean, filters fresh, and air out of the fuel system. The CP4 HP fuel pump is still the weak link on those motors, and it doesn't take much (just a little bit of water or DEF or air) loss in lubrication for them to put shavings into the fuel system, which can quickly lead to injector damage, melted cylinders, etc. Keeping the pumps properly lubricated is absolutely critical to the pumps durability.
There is a HUGE backlog for reman engines right now, primarily due to this reason. We have been cranking them out for Diamond Advantage (Navistar's aftermarket engine / component division) for the past 6 months. Hand-to-mouth. As fast as we get core and new parts, they get remaned and go out the door. CAT-Franklin (Ford's primary reman supplier) can't begin to keep up with demand.
Most sources I have seen are claiming a 7% failure rate within the warranty period. How much of that is due to contaminated fuel, improper maintenance, etc, who knows.