The dirty secret is that GM knew a LOT about the 6.5's reliability, but chose to deal with it via attrition, vs campaign recall, ie fix them when/if they break, if they make it past X miles then we won't have to fix them, plus DMAX already on dwg board, and no way a non common rail engine would ever meet tougher emissions they knew was coming. Same with other mfrs, 7.3 & 5.9 gone from production for same reason.
I'm living through same issues at work, converting MFI Diesel locomotives to EFI Diesel for tier 0, 1, & 2 compliance, will soon be working common rail fuel locomotives, and hybrid Diesel/electric/battery ones on not too distant horizon