I'm certainly not an engineer so I am the wrong guy to be asking, but IMO there is nothing wrong with running a quality CJ 4 oil. It may have been an issue when the CJ oils first came into play but how many engine failures have you seen period, let alone where engine oil was believed to be the culprit. the technology has come a long way that I just don't believe the flat tappet concern is valid anymore, they have developed other wear additives aside from the zddp additive found in CI4 oils. The CJ 4 test standards are more severe than the old CI4 requirement's and are superior in wear protection, soot related viscosity control (important even in non dpf equipped diesels) and viscosity retention from shearing, low temperature pumpability, and thermal protection To name a few.
I don't think there is necessarily a right or wrong answer as to which oil to run, but I think of it like this. Technology has come a long way since my 98.5 and your 99 has rolled off the assembly line. Take a look at the new Rams and how advanced they are compared to our trucks. Same as anything else, cell phones, appliances, medicine, etc. No way would I want to run an old Microsoft with windows 95 today. Fluids are all in the same boat, the technology has evolved so much I just don't see it being an issue. I don't have anything to back it up but I bet an overwhelming number of people are running CJ4 oils in their pre emissions trucks. Where are the failures? 9 Times out of 10 the engine will outlast the truck anyhow :-laf