I think TJ's are the newest old school vehicle with a lot of the better designs without as much of the stupidity. I think the R2.8 is a better engine, though different class, to work with after a decade than the 3.0 Ecodiesel, which has faults and it's going to be complicated and it's going to cost A LOT in the future.
However my wife likes the Gladiators and I can't stand the lack of low end from a v6 gas engine. The fact that you can get a 1/2 ton engine in a Gladiator is extremely interesting to me. The v8 Gladiator is just stupid so it's not really an option, but getting mid 20's MPG and having torque where it's useful is very very tempting, but on a vehicle I'd want to keep for a lifetime, the wiring is going to be a nightmare eventually and I don't see a lot of reman Eco-diesels out there, which is imperative if you want to keep a vehicle for a lifetime.
After a couple of decades all the wiring and stuff in these vehicles start becoming a nightmare. I've been just trying to get my 2003 Dodge Ram 2500 in better shape to match the 350k mi drivetrain and decided I wanted AC over the summer and ended up messing with wiring for a couple weeks, even bought a bidirectional scan tool to help hunt down the problems. I decided I wanted to make the audio functional again and I got interested in Apple Carplay and On X maps on a big screen and now I'm weeks into trying to rewire almost every single speaker and the way they do wiring harnesses, this is extremely difficult and the intermittent wiring problems suck to hunt down with the way all these dashes and stuff are mounted and the plastic connectors are brittle.
And IMO the wiring of a 2003 looks simple compared to all the BS on even newer trucks and I really like picking out a vehicle for a lifetime and not just buying and selling before it grenades on me, but I don't even think that's going to be as possible going forward with all the new designs that are absolutely nonsense. It really grates at me too that if you go overseas to places that aren't crazy regulated you can buy pretty much a solid 70's vehicle with the best 90's designs and equipment and manufacturing. It's crazy how much other countries just want their stuff to work and get from A to B through difficult terrain. When I was in India new vehicles were like $15k for top of the line compared to $30k in the US because of all the regulations we have and for some reason OEMs aren't ever trying to make their vehicles better, just look different and lick the boot of CA regulators.