WELCOME to our forums.
Your '93 W250 has an A518 (AKA: 46RH) transmission. It amounts to a 727 with an overdrive section added. In fact, many of the parts from a 727 are interchangeable with the later Dodge 46RH, 47RH & RE, as well as the 48RE transmissions.
Typically those transmissions for the Diesels (and V10) trucks include heavier planetary gear-sets, etc as compared to the gas versions. Further, the diesel versions include a different governor assembly tailored to the diesel's lower engine RPM ( a gas transmission behind a diesel will result in the diesel having to rev excessively too high before the trans gets around to shifting gears.