International Trucks tried making their own engine that was " smog legal " without having to use DEF / SCF technology, which was attractive to trucking companies that were fearful of the ( or any ) new technology, even though PACCAR ( Peterbilt / Kenworth ) had already been building emissions control - equipped trucks ( DAF ) in Europe for several years. International was never quite able to make their Class 7 & 8 tractors run clean enough to pass emissions; however they used emissions credits from their Class 5 & 6 trucks that ran cleaner than was required at the time. They finally gave up, and began using smog legal engines from Cummins, after lotsa butt - kissing from walking away from Cummins for several years.
I recall that 2014 was the first year of current heavy truck DEF & SCF emissions controls, which would explain the 1995 era trucks having few issues.