Repeated Turbo Failures

[JMBT]

Even with the good maintenance practices he stated above if the truck still has the mandate at 750+k it would be nearly impossible to keep the intake/exhaust systems happy outside of making the EGR tune up a weekly practice. An engine with those miles is going to have some blow by and maybe an internal weep here and there, and exhaust or boost leak, or something of that nature that is too small to be detected. Any of those things will play hell on the DPF and EGR systems and it will get progressively worse as it ages. Filling up the filter with ash and causing more exhaust pressure.
I would say you have two options: 1. A brand new holset turbo and a trip to Mr Hagg, for a demandate. Or 2. Buy the brand new Chinese knock off from AW turbos for about $700. And just plan on replacing it every year. They are cheap knock offs but you are going to kill any turbo you put on it at that point anyway.

Another thing to consider, if you have any oil leaking into exhaust manifold, like say from valve seals leaking. The oil combined with soot will quickly plug up the tiny tube that feeds the exhaust pressure sensor, causing a faulty reading and pop there goes your new turbo seals.