My buddy did a Cummins 2.8 conversion on his early Bronco. He's running 35's IIRC, and he is pretty happy with the 2.8. It crawls along nicely, and is torquey. I don't think mileage is spectacular, as the main limit is aerodynamics, and an early Bronco on 35's is, well, not aerodynamic in any way. Still better than it was with the 351 that was in it... The same would apply to a Wrangler, which would likely struggle to hit the low 20's if converted, unless you routinely travel large distances at 55 or 60mph max. I do think he's happy with the power, and there are now higher output calibrations that can be installed if you want even more...
My wife had with a CRD Liberty when we met in 2011, and we kept it until about 2015. It was a good powertrain, excepting the drainback issues with the 545RFE by 150k or so. I hated the Limited seats in her Liberty, but it was indeed a pleasure to drive. Unfortunately, the liberty powertrain is very difficult to "swap" without the ability to do some significant re-calibration because it gets vehicle speed over the can bus from the ABS module IIRC. Green Diesel used to be able to help with the calibration end of things, but I'm not sure they'll even touch one these days with EPA concerns. I believe there was an export diesel JK almost since the beginning, but I don't think it used the VM, so swapping a KJ VM into a JK is not going to be easy. Since people couldn't be bothered to sign the petition to change the import restrictions from 25 years to 15 years a couple years ago, importing a diesel JK is still a decade away.
Warning, a bit off topic...
When I worked at Jeep in the late 90's and early 2000's, I spent some time in a 2.5l VM turbo diesel Cherokee, which was assembled here in the US, but for export only. The diesel was only available with a 5 speed manual. While it was only 110 or so hp, it had 330ftlbs of torque IIRC, and IMO, was a GREAT powertrain for a relatively stock Cherokee. It was a bit "buzzy" on the highway, but I recall it getting 24or 25mpg on a trip down into IN. (probably @ 65mph...) I really wanted that powertrain in a TJ, but Diamler never chose to package it for TJ, even for export. For those of us interested, '97 Cherokees should be elligible for import now, but finding a nice enough one to justify shipping it here will be tricky. Still not a great swap for a bigger Jeep like the JK though.
The same 2.5L VM was also used in chrysler minivans and the ZJ in export markets, starting I believe around 1995. Either of those might be a doner for a TJ as well. The VM 2.5 was an indirect injection engine. It later recieved common rail control and a bit of an over-bore to become the KJ 2.8L CRD. At one time, I had thoughts of getting the heads, IP, and ECM from a euro 2.5 and using the parts to convert a 2.8L CRD to old school injection, which would work in my manual trans TJ...
Finally, the diesel that AEV put in a TJ back in the mid-2000's was the VM out of a Cherokee. (Possibly, the one I drove, as I think that was one of the last diesel cherokees in the development fleet...) I think AEV still has that TJ...
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