This engine keeps eating HPOP, three in the last 15 months, this last one lasted 500 miles after complete engine rebuild in a shop that I have never had any issue's with in 20 years. The last one was replaced under warranty by local International dealer after the new one they installed failed, but this time they are refusing to warranty the pump or repair. Any and all input is welcome, the truck is off to auction and although it starts it goes into limp mode after a few minutes before shutting down completely.
In general, I find that engines that run injectors with high pressure oil are the most problematic to diagnose. What, exactly is failing on the HPOP? It is a pretty simple thing. Gear turns, oil is pumped. Have they looked at the LPOP?
How are the HPOP's failing? No start, low power, Is this engine a DT466? If so the oil that is supplied to the HPOP is unfiltered. You could have something failing in the engine creating metal particles in the oil. Cut the oil filter open and look for particles.
People will be able to help you better, the more info that you give us. For example, we don't have any idea even what engine is in your truck.