overseas JKs have a 2.8l diesel. who makes that diesel and i wonder if you can get one here...
Around here, there are also Jeep diesels, as well as Toyota, BMW, Mercedes Benz, Nissan, and just about every manufacturer (including Ford). The thing is that you want an efficient diesel, because they are not all the same. The reason I like the BMW is that it is LIGHT, so if you reduce weight, and increase power, the Jeep would all of the sudden become a very nice toy to have around. Also, keep in mind Diesel engines have more low-end torque, which is also better than the 2.5L.
If I were to go to another manufacturer, I would stay away from the Jeep engine and just drop one from Toyota (probably the one found in their HiLux pickups and Fortuner SUV's, which is a 3.0L Turbo Diesel) along with the rest of the drive train (TC and tranny). But that means new DS and a whole lot of other mods which you would not have with the 1.9L VW engine.