The first gen is a different motor than the newer 2nd (actually 3rd) gen motor in the Gladiator you experienced. They are not at all equivalent, with 80% parts differing. The older motor is the VM Motori L630. It was made by a different company that was later integrated into Fiat, called VM. VM was not a very good company. They made stuff with poor build quality and somewhat questionable Italian bleeding-edge engineering.
Note that the old 1st gen motor has emissions systems that are crap and go wrong frequently... even without DEF being required. I would rather have a DEF system that worked than a non-DEF EGR computerized system that breaks frequently and is expensive to fix and difficult and illegal to bypass.
Due to the emissions, the driveability of the older motor is poor without a tune. It doesn't perform the same in real life as the FIAT motor in the Gladiator you rode in. It is more like having an on/off switch instead of a throttle-- whereas the FIAT motor has actual throttle response. Tunes fix this somewhat, but even tuned it is not as responsive as the newer FIAT engine is stock. One guy I know with the older tuned eco-diesel described it as a "toy" compared to the test ride he took in a RAM with the new engine.
The parts cost and availability are horrid. You will wait for parts from the 2 main US Fiat warehouses on a good day. On a bad day, it is back-ordered from Italy and your ETA is two months. You are not getting anything more than an oil filter at the local ONapaZone, it is dealer only. You will need a "special tool" to work on just about anything on a VM diesel. Most independent diesel mechanics hate these things because they are difficult to work on and require expensive vehicle specific tooling that they don't want to buy to support the 2 of these things driving around their major city. Parts cost are insane, even compared to typical medium duty commercial diesel engine costs.
If you are dead set on a modern diesel, look at the Cummins 2.8 crate motor, a TDI, a Benz, or the new Fiat motor from a wreck-- and buy the whole wreck and not just the engine. Don't bother with anything else made by VM. This includes the "Duramax" re-badged eco-diesel they put in the Chevy Colorado's.
If you are not dead set on a modern diesel, please consider older and industrial diesel engines instead. The industrial engines have much better reliability and are more simple to swap and repair, but have less power stock and more noise and heavy. If that is not your bag and you care only about power, then just go with whatever gasser swap you are partial to and you will save money and avoid many headaches.
