A few points to ponder.
- 6.0 and 6.4 Ford diesels are junk, and are priced accordingly used. A low price does not always equate to a good value. There are options for "bulletproofing" these engines but I don't know what they cost or how effective those preventative fixes are.
- Since you're shopping used trucks, I would ignore the 3/4 ton vs 1 ton distinction. I don't think there were any functional differences in any of the big 3 in those years beyond (sometimes) rear spring setups, and you can supplement that with bags or timbrens if necessary. You're already looking at a limited inventory of trucks so there's no reason to artificially limit even more.
- Emission systems can be problematic in the years you are looking at. Consider whether deleting is an option if that's something you're comfortable with. I don't think Ram went to DEF until about 2013 and there were some issues prior to that. I'm not as sure on the timelines with the Duramax or Powerstroke.
- None of the newer diesels are as loud as your '94, not even close.