I have a 5.9 in a 94 2500 with 384k miles, stock with the exception of bigger injectors and Airfilter. I have had zero issues in the 4 years I have had it, servicing is mostly on time with quality oil. Every tank gets fuel treatment so I don't believe that is the issue. The problem is it will randomly shut off and then will restart, it is getting worse and it will also lose power after getting up to temperature in 3rd and O/D.