The DT/DTA360 is regarded by most as the "best" medium diesel ever, it's larger brother the DT/DTA466 was available in the higher HP/Tq ratings and so are more common - MUCH more common. Interestingly, about 70% of their parts interchange, obviously some of the castings and stuff don't, but parts are readily available for either. Point is, not to discount a good deal on EITHER.
Everything changed in 1994 with the advent of electronics, the engines last longer but the cost per mile (or year) actually goes up because of the wiring, sensors etc that is affected by time even if they sit. FF to 2004 and things got even worse, performance of all diesels went WAY UP, but the reliability has not been favorable for any of the brands.
If you want a nearly bullet proof diesel, for reasons that are well beyond this thread, it would be an IH, DT/DTA 466 with an Eaton transmission and air brakes; given the loads you want it to work with.
Having said all that, I would not pass up a Ford 429, GM 366/427 or IH 392 gasser in that size truck for the right price (~1/2 of a diesel). Again, RUN from any manual that does not say EATON on it!!!!!
If you are at all masochistic and have excellent luck in Vegas, you *could* opt for an older Ford or GM with an 8.2L diesel, they sell for almost gasser money and with good reason
