The RE's work pretty well, and they were fairly cheap too. I paid $137/ea when I ditched my Rough Country springs last summer. Rough Country springs ride ok too and definitely flex great, but they have a tendency to sag... I had two sets of rears sag. Not
everyone has had theirs sag but again it's possible.
If you look on this page there's a thread I started called "Finally!..." with pics of my new KM2's on my rig. I clear 35's in the rear no problem, the front do hit the fenders but the springs are virtually flat when they rub, so some bumstops are in order.
If I was going to swap out the transmission, I'd highly look into swapping in a NV3550 5-speed. The NV3550 is pretty common swap and since the AX-15 and the NV3550 use the same bolt pattern, you should be able to swap between them.
I'm not certain if you can use a NSG-370 6 speed manual but that's another I'd look into. Although, I think it might have an integrated bellhousing which will make it not work.
BTW: thanks for your service.
I think swapping the NSG-370 would be somewhat of a challenge. A guy on JF was swapping one behind his YJ w/ a 6 cyl and it took him some time to get it right but he eventually did... I think. I'd love to do this swap but if it's possible it's got to be a real PITA. I think it'd be awesome to have this tranny with my gearing and 35's, it'd kick ass to have for driving to and from Tahoe when I get in to the mountains.