Check the RPO code sticker on the passenger door. That will give you the axle ratio. GU6 is 3.42, GT4 is 3.73, GT5 is 4:10. It'll definitely be a G-code, so if not those, then google the code you have and see what it is. It should also say G80 in your case...
If you have 3.73's, then you're not doing bad. If you have 16" wheels already, some 265/75R16's would probably be OK, and a good bit wider and a bit taller than your current tires. If you have 15" wheels, then some 31x10.50's would be a step up. 30x9.50's a bit smaller but better fit probably... Or you can go aftermarket, but stay with 16" wheels at the biggest for best offroad performance. The more sidewall the better!!
You would be surprised how much better your 2wd van will do in soft conditions with less tire pressure. I once stuck an empty 2500 cargo van in a sandy area working on the traction control programming. I let the rear tires down to about 15psi and drove right out like it hadn't even been stuck! That was with 245/75R16's, and the fronts were still at 60psi. I suspect that at 30psi all around, I wouldn't have been able to get it stuck. How low you have to go is a function of tire size and weight, but a little experimenting will tell you how low you need to be in general for soft terrain. Even though it's only 2wd, airing down the front tires too will help much more than airing down just the rears. So long as you have a way to air back up, it's much easier on the truck and the trail than getting a big run at it and hoping for the best...
If you're in AZ, then you know what happens to roads in the SW when it rains. Cable chains will get you out when even 4wd has trouble. Airing down will do wonders for that situation too, as it allows the tires to conform to the terrain and shed a bit of mud, rather than being a hard round slick that makes a slight depression and then can't get out... It pains me to see people dug right in with chains on in soft conditions because they didn't know enough to air down and get the tires to float...
The G80 is a bit of a limited slip normally, and I would recommend against running synthetic gear lube, as it works better with a bit more friction from normal gear lube. Friction modifier also a no-no for the G80. If one tire loses traction and begins to spin, the G80 has a governor that latches and causes the clutches to bind up fully, forcing both tires to spin until torque is reversed. Changing to any other diff, including an easy locker of any kind means changing the carrier, which is fairly expensive, especially if you don't have to change gears. On the other hand, if your RPO sticker doesn't say G80, but you have GT4, then dropping in an easy locker is much, uh, easier...
A winch is nice if there are trees around. So are front and rear tow points, though the aftermarket receivers for these vans hang down quite low... For most desert use, you really shouldn't be stuck if you adjust tire pressure accordingly. Your conversion van has quite a bit of weight on the rear axle, and that should keep you moving in all but the roughest conditions.
