Actually you have 4 O2 Sensors, I was just replying to that particular code you posted. The plug-in for that sensor is located on the body support rib just above and to the left of it. You might want to check the plug-in first to see if it is making a good connection or not, it does happen from time to time (bad connection). My best advice here if your going to try to replace this yourself, is to buy an O2 sensor socket to remove it.
They can be very difficult to remove at times. If you can get a source of heat to apply to the exhaust pipe and a can of lubricant, then just work the sensor out slowly. It will more than likely just come out about a half a turn then stop. When that happens don't try to force it any further, just spray some lubricant on the threads and turn it back in, then try to remove it again. This will take about 5 or 6 times doing this procedure before it actually comes out.
As for the Astro/Safari reliability, I think they are very reliable overall. It's just how each owner drives them and maintains them that really plays an important roll in dependability. Gas mileage can be very good with these vans if you keep your foot out of it and everything relating to gas mileage is maintained and adjusted regularly (tire pressure, wheel alignment, etc.). I get 26-28 hwy now with the bigger tires on and different gear ratio, but I use to get 30-32 hwy with mine (really), easy driving of course . People don't believe it when I tell them this, but hey, I don't really care, I'm saving the money, not them,hehe.
A family member has a Dodge Caravan with the 3.3. You might want to have a look at the rear plugs if you think the 4.3s are hard to do, hehe. I like the Caravans seats (comfortable) and handling. I don't like the room or the nose heavy feel it has to it though. They do get up and go at bottom end (rpms), but top end has a lot to be desired. His has been very reliable to this point and he is very happy with it though and I guess that's what's important. You will never carry anywhere near the load these vans do with the front wheel drive uni-body set-up and they do struggle when you have 3 or 4 passengers in them as well, but this applies to any front wheel drive van.
All Data is very good and what a lot of the shops use as a reference for repairs.
This site is mainly based on sharing each others experiences to help each other out and look forward to yours.