Hmm, my taste leans to the Sub. But not with a RTT. You got enough space inside the burb to haul a lot and still sleep inside it. That does depend on how many are going to with you too.
Ideally I'd combine some of the parts you got. Namely the nv4500 trans from the '92 truck into the burb. Two main pro's that come from that. First the '92 4500 is the early deep first gear version, which really comes in handy off road. The next item is the OD. Having OD will help on the highway and eek out a little better fuel economy.
The downside is making the swap happen. You'll need to find a clutch/brake pedal setup for the manual trans, which needs to be for a hydraulic clutch. They are out there, but they are typically pricy. Then you have to source a bellhousing since the '92 will have the clutch slave cylinder on the same side as your front driveshaft. It can work if you have enough lift or you pony up the funds for an Advanced Adaptor's conversion bellhousing. It would allow the use of the stock squarebody clucth hydrualic system.
I'm not going to deny, it's not the easiest thing to do, but it's very rewarding in making an old truck much more usable.